Explanations April



A beetle’s wings are rarely visible. Hidden behind armored shields on the creature’s back and unfolding in whirring sheets, whisking their clumsy owners away from danger.


B. back, they unfold
C. back to unfold
D. back and unfold


The original version of the underlined portion creates a fragment because the statement does not contain a main (independent) clause: neither Hidden behind shields on the creature’s back, nor unfolding in whirring sheets, whisking their clumsy owners away from danger can stand on its own as a sentence. That eliminates (A).

(C) and (D) are incorrect for a similar reason: each of these answers creates a dependent clause that by definition cannot stand on its own as a sentence. (B) is correct because the words they unfold act as a subject and verb that create an independent clause (they unfold in whirring sheets) and turn the statement into a complete sentence.





In the first half of the twentieth century, tornadoes were said so unpredictable that in order to prevent mass hysteria, the word “tornado” was forbidden from weather forecasts. Progress on the forecasting front moved slowly until the 1970s, when the first Doppler radar allowed scientists to track a storm’s development and spot the signs of a developing twister.


B. considered
C. viewed
D. described


(A) is incorrect because something is said to be x, but to be does not appear. (C) and (D) are incorrect for a similar reason: described and viewed must be followed by as, but this word is also missing. Only (B) is an acceptable option: although considered can be followed by to be, those words are not required. It is correct to say that something is considered x.





The correlation between bad moods and negative judgments allows people to make informed guesses about how others are feeling by observing their actions and choices.


B. judgments allow
C. judgments have allowed
D. judgments, which allow


Don’t get fooled by the plural noun judgments, which appears immediately before the verb (allows). In reality, that noun belongs to the prepositional phrase between bad moods and negative judgments, which is placed between the subject (The correlation) and the verb. Correlation is singular, and so a singular (-s) verb is required. That elimates (B) and (C). (D) can be eliminated as well because this answer creates a fragment: although the plural verb allow agrees with judgments, it also “belongs” to which rather than to the subject of the sentence, The correlation. As a result, the sentence is missing a main verb. (A) correctly supplies a singular main verb (allows) that corresponds to the subject of the sentence.





The original Shinkansen, or bullet train, connects the largest Japanese cities of Tokyo and Osaka, is the world’s busiest high-speed rail line. Carrying 151 million passengers per year, it has transported more travelers than any other high-speed line in the world.


B. train connects
C. train connects:
D. train, which connects


To answer this question, you must consider the sentence as a whole; the underlined section alone does not give you enough information to determine the correct option. When considered independently, the underlined portion makes sense; however, the construction Osaka, is later in the sentence signals the end of a non-essential clause. In fact, the sentence contains two non-essential clauses placed back to back: or bullet train and (which) connects the largest cities of Tokyo and Osaka.

To simplify the sentence and reveal the error, cross out the first non-essential clause: The original Shinkansen…connects the largest Japanese cities of Tokyo and Osaka, is the world’s busiest high-speed rail line. Clearly, that does not work grammatically.

Because the end of the sentence cannot be changed, the beginning must be altered to include the start of a non-essential clause. This type of clause cannot begin with a verb; instead, it must begin with a relative pronoun (which). Now, when the first non-essential clause is crossed out, the sentence makes grammatical sense: The original Shinkansen…which connects the largest Japanese cities of Tokyo and Osaka, is the world’s busiest high-speed rail line. That makes (D) correct.





In the mid-nineteenth century, the Oregon Trail was the principle pathway for immigrants seeking land and opportunity on the American frontier. From its main departure points in Missouri, the grueling overland route stretched 2,000 miles over the Great Plains and the Continental Divide, finally ending in the fertile Willamette Valley or the gold fields of California.


B. principal pathway for
C. principle pathway to
D. principal pathway to


Based on the context, the underlined portion must be referring to the main pathway, i.e., the principal pathway. A “principle” is a fundamental rule or doctrine. That eliminates (A) and (C). Logically, the Oregon Trail must have been a pathway for immigrants rather than to (toward) them. That eliminates (D) and makes (B) the answer.





A snowflake begins to form when an extremely cold water droplet freezes onto a pollen or dust particle in the sky, this creates an ice crystal. As the ice crystal falls to the ground, water vapor freezes onto the primary crystal, building new crystals—the six arms of the snowflake.


B. sky and create
C. sky, creating
D. sky; creating


(A) creates a comma splice: two complete sentences separated by only a comma (tip-off: comma + this). When plugged in, (B) creates a coherent sentence but a subject-verb disagreement: the subject of the verb is an extremely cold water droplet, singular, whereas create is plural. Creates (parallel to freezes) must be used instead. (D) is incorrect because a semicolon can only be placed between two complete sentences, and creating an ice crystal is not a sentence. (Note that as a general rule, an -ing word should not follow a semicolon.) An -ing word (creating) can, however, be placed after a comma to join an independent and a dependent clause. That makes (C) correct.





Not so long ago, astronomers didn’t know if there were planets outside our solar system or, if there were, whether it could ever be found. But starting with the 1995 discovery of a planet circling the sun-like star 51 Pegasi, there has been a revolution.


B. this
C. they
D. DELETE the underlined word.


The only noun in the sentence to which the underlined pronoun could refer is planets, plural, so the correct answer must be plural as well. It and this are both singular, so (A) and (B) can be eliminated. (D) does not fit either because the sentence no longer makes grammatical sense when the underlined word is eliminated — a pronoun is needed to refer back to planets. They is plural and agrees with planets, making (C) correct.





In recent years, robotics has found its way into our everyday lives, changing them in fundamental ways. Designers have a central role to play in this process, which they shape the interfaces between humans and machines.


B. process:
C. process,
D. process that


(A) is incorrect because the word which is unnecessary and creates a nonsense construction. Because which is placed immediately after process, it appears to refer back to process; however, the information that follows (they shape the interfaces between humans and machines) refers to designers. (D) creates the exact same error — it merely replaces which with that. (C) is incorrect because the comma after process places a comma before they, creating a comma splice: two complete sentences separated by only a comma. (B) correctly uses a colon to separate two complete sentences and signal that the second sentence explains the first — that is, the second sentence describes the central role in robotics played by designers.





Researchers at the University of Maryland have developed a super-lightweight insulating material that, they claim, could prove to be a superior alternative to styrofoam. The material, made from tiny wood fibers, is called nanowood.


B. material, that they
C. material that they
D. material and they


Although in most circumstances, no comma should be placed either before or after that, this question is the exception. The key to understanding the logic of the sentence is to recognize that the words they claim, which appear after that, can function as a non-essential clause and must therefore be surrounded by commas. When the clause is removed, the sentence still makes sense: Researchers at the University of Maryland have developed a super-lightweight insulating material that could prove to be a superior alternative to styrofoam. That makes (A) the answer.





Hummingbirds have long intrigued scientists. Their wings can beat 80 times a second, and their hearts can beat more than 1,000 times a minute. They consume nothing but nectar—a sugar- and nutrient-rich liquid produced by plants—they are capable of packing on 40 percent of their body weight in fat for migration.


B. Because they
C. Although they
D. Since they


Be careful not to focus only on the beginning of the sentence; the information you need to answer the question is elsewhere. Start by eliminating the non-essential information between the dashes to simplify the sentence: They consume nothing but nectar they are capable of packing on 40 percent of their body weight in fat for migration. What remains is clearly a run-on. The first clause must be altered so that it becomes dependent, which means that a transition is required at the beginning of the sentence.

Next, consider what the two statements are saying: 1) Hummingbirds consume only nectar; 2) they can gain up to 40% of their body weight. Because and since are synonyms, so by default, neither (B) nor (D) can be correct. That leaves (C): although correctly conveys the contrast between the single type of food consumed by hummingbirds and the enormous amount of weight they are able to gain.





The Megalodon, a prehistoric ancestor of the modern shark, had a bite force of 12 to 20 tons, somewhere between six and ten times stronger than a modern Great White.


B. then a modern Great White.
C. than that of a modern Great White.
D. than those of a modern Great White.


(A) incorrectly compares the Megalodon’s bite force (thing) to a modern Great White (animal). Because the first side of the comparison cannot be changed, the second side must be changed so that the bite force of the Megalodon is compared to the bite force of the Great White. (B) contains the same error as (A) and also wrongly uses then instead of than to form the comparison. (D) is incorrect as well because it replaces the singular bite force with the plural pronoun those. (C) correctly uses the singular pronoun that to replace the singular noun bite force. (That of = the bite force of.)





Steve Desch, an astrophysicist at the University of Arizona, can see the future of exoplanet research, and it’s not pretty. Imagine, he says, that astronomers use NASA’s upcoming James Webb Space Telescope to scour the atmosphere of an Earth-mass world for signs of life. They might chase hints of atmospheric oxygen for years before realizing they were false positives produced by geological activity instead of living things.


As it is used in the passage, “scour” most nearly means


A. cleanse
B. consume
C. search
D. burnish


Consider the context: the passage is talking about astronomers who are using a telescope to look carefully for, i.e., search, the atmosphere of a planet for indications of life. Even if you don’t know what scour means, that information is most directly consistent with (B). Cleanse, the literal meaning of scour, consume (eat or use up) and burnish (polish) all do not make sense.





With the car windows down on the first warm day of spring, the urge is unshakable. You extend your arm into the wind, tracing the city skyline in a natural motion somewhere between swimming and waving. As you move your hand, altering the flow of the air. The redirected air, in turn, exerts a force on your hand.


B. hand and alter
C. hand, you alter
D. hand to alter


The original version of the underlined portion creates a fragment because the statement does not contain a main (independent) clause: neither As you move your hand, nor altering the flow of air can stand on its own as a sentence. That eliminates (A). (B) and (D) are incorrect for a similar reason: both of these answers create a single clause that begins with as (a subordinating conjunction) and thus cannot stand on their own as sentences. (C) is correct because the words you alter act as a subject and verb that turn the second clause — the information after the comma — into a complete sentence (you alter the flow of air).





Although the concept of sleep-learning, also referred to as hypnopaedia, has been discredited, neuroscientists are now discovering ways to use stimuli such as sound cues during sleep to strengthen peoples’ memories.


B. peoples memories’.
C. people’s memories.
D. people’s memory’s.


When a question tests two consecutive nouns with apostrophes, the standard pattern is that the first noun is possessive (apostrophe) and the second is plural (no apostrophe). That is the case here: the underlined portion refers to memories belonging to people, so the first noun is possessive. (B) can be eliminated because peoples is plural rather than possessive, so the question becomes whether the apostrophe should be placed before or after -s. For regular nouns, the plural possessive is formed by adding –s + apostrophe, but people, the plural of person, is irregular. When a plural noun is irregular, the plural possessive is formed by adding apostrophe + -s, so (A) can be eliminated. (D) is incorrect as well because memory’s is the singular possessive form. (C) correctly forms the possessive of the first noun by adding apostrophe + -s and the plural of the second by adding -ies. People’s memories = memories of people.





Once upon a time, it seems that Mars had oceans. However, the exact appearance of these bodies of surface water is a matter of intense debate. Most evidence points towards the deep past, some 4 billion years ago, as the age where Mars could have held marine environments. Since then, the red planet has most likely been cold and arid, with only the occasional shift of climate conditions.


B. in which
C. which
D. in that


Where can only be used to refer to places, not times/time period, so (A) can be eliminated. (C) is incorrect because which alone should not be used to refer to a time period either. (D) is incorrect because in that is a synonym for because, a meaning that does not make sense in this context. The only two options are when and in which. Because when does not appear as a choice, in which must be used. That makes (B) correct.





Baseball has a long and rich history in Japanese-American diplomacy. After the sport was introduced to Japan in the 1870s by the American educator Horace Wilson, it became an important part of Japanese popular culture. Over time, baseball has served as a unifier, bringing together the people of two nations with very different histories and cultures.


B. educator, Horace Wilson
C. educator, Horace Wilson,
D. educator Horace Wilson


When a name appears in the middle of a sentence, as is the case here, it is always incorrect to place a comma only before the name. As a result, (B) can be eliminated automatically. Placing a comma both before and after a name indicates that the name is being used non-essentially and can be crossed out of the sentence without disturbing its basic structure or meaning. To check (C), cross out Horace Wilson and read the sentence without those words: After the sport was introduced to Japan in the 1870s by the American educator… it became an important part of Japanese popular culture. No, it does not make sense to refer to the American educator without providing his name. Although the sentence is acceptable grammatically, it does not work from a meaning standpoint. Now, the question is whether a comma is needed after the name. In this case, the answer is yes: the sentence begins with a dependent clause (After the sport was introduced to Japan in the 1870s by the American educator Horace Wilson) that is then followed by an independent clause (it became an important part of Japanese popular culture). When an independent clause follows a dependent clause this way, a comma must be used to separate them. That makes the answer (A).





One of the most renowned architects of the twentieth century, Frank Lloyd Wright was the pioneer of the Prairie School movement and he developed the Usonian home, his unique vision for urban planning in the United States.


B. and developing
C. the developer of
D. had developed


The sentence indicates that Wright was two things: the pioneer of the Prairie School movement of architecture and __________. To keep the sentence parallel, the two sides must match. The non-underlined portion of the sentence contains a noun (pioneer), so the underlined portion of the sentence must contain a noun as well (developer). (C) is the only answer to include this construction, so it is correct. Note that although it is technically grammatically acceptable, if not parallel, (A) does not work because the information that follows and is a complete sentence, and so a comma is required before that word.





In terms of intelligence, the octopus stands far above most other animals. During one really cool study, researchers tested whether this creature is able to distinguish between different people. Two individuals interacted with an octopus, with one acting extremely friendly and another seeming cold and standoffish. Later, when the two people entered the octopus’s living area, the octopus ignored the impersonal one in favor of the friendlier guest.


B. awesome
C. intriguing
D. totally neat


This question is testing register, or formal vs. informal language. Really cool, awesome, and totally neat are all overly casual when compared to the rest of the passage. Only intriguing is consistent with its moderately serious tone. That makes (C) the answer.





In the early days of mariachi music, players dressed informally. With increased employment opportunities and more formal presentations, however, uniforms became common. When mariachis first acquired the purchasing power to dress their groups in uniforms, the apparel they had chose most often was the charro suit, which consisted of fitted trousers, a short jacket, and an embroidered belt.


B. have chosen
C. chose
D. choose


All of the non-underlined verbs in the passage are in the simple past tense (became, acquired, was, consisted), so the underlined verb must be in this tense as well. (A) is not only in the past perfect (had + past participle), but it also incorrectly forms this tense: the simple past chose rather than the past participle chosen appears after had. In (B), the present perfect (has/have + past participle) is correctly constructed, but this tense is not consistent with the rest of the verbs in the passage. (D) is incorrect because choose is the present tense, which again does not fit. (C) correctly provides the simple past form, chose.





You can probably recall a situation, in sports or otherwise, in which you felt like you had momentum on your side: your body was in sync, your mind was focused, and you had a high level of confidence. In these moments of flow, success feels inevitable, and effortless.


B. you had a high confidence level.
C. your high confidence level.
D. your level of confidence was high.


The underlined portion is the third item in a list, and so it must be presented in the same format as the first two items. Both of those items begin with your, so the third item must begin this way as well. That eliminates (A) and (B). (C) is incorrect as well because each of the two previous items contains the pattern your noun + verb, and this answer does not contain a verb. (D) correctly begins the third item with your and includes a verb (was), maintaining the pattern used in the first two items.





Despite decades of research, the sun remains an enigma. Every 11 years or so its activity spikes, creating flares and coronal mass ejections—the plasma-spewing eruptions that shower Earth with charged particles and beautiful auroral displays. Then, however, the so-called solar maximum fades toward solar minimum, and the sun’s surface grows eerie quiet.


B. eerily quiet.
C. eerie quietly.
D. eerily quietly.


Logically, the sun’s surface must grow (i.e., become) quiet, not quietly, so the second underlined word must be an adjective. That eliminates (C) and (D). The adjective must in turn be modified by an adverb. (How quiet does the sun’s surface become? Eerily quiet). Note that because the adjective eerie already ends in an –ee sound, –ily must be added to form the adverb. (B) is thus correct.





According to research, people are generally biased toward believing that information is true. (After all, most things that we read or hear are true.) In fact, there’s some evidence that we initially process all statements as true and that cognitive effort is required to mentally mark some of them as false.


In the last sentence, the word “mark” most nearly means


A. distort
B. label
C. transmit
D. inscribe


The structure of the sentence provides a subtle but important clue to the meaning of the underlined word. The construction we initially process all statements as true and that cognitive effort is required to mentally mark some of them as false indicates that the word in question must be generally consistent with the idea of processing or perceiving. The only option that makes sense in that context is label: the sentence is saying that the brain requires extra information to assign things to the “false” category, i.e., to label them as such. Transmit (send) and inscribe (engrave) do not fit at all, but be careful with distort: something that is false does indeed provide a distorted picture, but the underlined word itself does not actually have this meaning.





It has taken a while for scientists to piece together the riddle of just when and where cats first became domesticated. In many cases, this type of question can be easily answered by the archaeological record, but in this instance the matter is complicated by the fact that wild cats and domesticated cats have remarkably similar skeletons.


All of the following placements for the underlined word would be acceptable EXCEPT


A. where it is now.
B. after the word can.
C. after the word answered.
D. after the word the.


Easily is an adverb and can only modify a verb. Because modifiers must be placed next to the words they modify, the three acceptable answers must place easily next to verbs. In (A), be is a verb; in (B), can is a verb; and in (C), answered is a verb. Only (D) does not place easily either before or after a verb (the, archaeological). Because the question asks you to identify which placement would NOT be acceptable, (D) is correct.





Knowing that an employee demonstrates high levels of conscientiousness won’t tell you whether his or her work will be careful or sloppy if you inspect it at a particular moment. But if a large company hires hundreds of employees which are all conscientious, this strategy will likely pay off with a small but consistent average increase in careful work.


B. who
C. whom
D. DELETE the underlined word.


The underlined pronoun refers to employees, i.e., people. Which should be used to refer to things only, so (A) can be eliminated. (C) is incorrect because whom would be placed right before the verb are, and as a rule, whom should not come before a verb. (D) is incorrect because deleting the underlined word would create a nonsense construction (But if a large company hires hundreds of employees are all conscientious…) — a pronoun is needed to refer back to employees. (B) correctly uses who to refer to people. Unlike whom, this pronoun can be placed before a verb.





Growing hardy and plentiful on short, stout bushes, the prairie cherry’s ornamental blooms and glossy leaves produce a deep-red fruit that is less sweet than the traditional cherry, and can be eaten straight from the tree.


B. cherry, and can be eaten straight,
C. cherry and can be eaten straight
D. cherry and can be eaten straight,


Comma + and = period, but a period cannot be plugged in without creating nonsense: Growing hardy and plentiful on short, stout bushes, the prairie cherry’s ornamental blooms and glossy leaves produce a deep-red fruit that is less sweet than the traditional cherry. Can be eaten straight from the tree. As a result, the comma is unnecessary, and (A) and (B) can be eliminated. (D) is incorrect as well because the comma after straight incorrectly places a comma before a preposition (from). (C) is correct because no punctuation is needed in the underlined section.





During the early days of space travel, astronauts squeezed most of their meals out of tubes. A sugary, orange-flavored drink, sold commercially as Tang, was considered a tasty treat. Food was fuel, and little more. Meals are stored in locker trays held by a net so they won’t float away. In fact astronauts can dine on a variety of freeze-dried meals using regular forks and spoons. And, for a few years, crews in the International Space Station (ISS) have been able to savor a taste of food that’s actually fresh.


Which of the following provides the best transition between the previous sentence and the sentence that follows?


B. Salt and pepper are available, but only in liquid form.
C. Today, eating in space has become much less of a chore.
D. Being in space can put a damper on an astronaut’s appetite.


Although the question asks about the underlined portion in terms of the previous and following sentences, you may find it helpful to take more information into account. The beginning of the passage focuses on the fact that eating in space had little resemblance to that act on Earth and involved unappealing food. The latter part of the passage emphasizes that more recently, astronauts’ food has been considerably improved. The underlined portion must therefore set up the contrast between those two ideas and introduce the fact that eating in space is more pleasant than it used to be. In other words, it “has become much less of a chore.” That makes the answer (C). All the other options are off-topic.





Fraudulent images have been around for as long as photography itself, but Photoshop ushered image doctoring into the digital age. Now, artificial intelligence is poised to take photographic fakery to a new level of sophistication thanks to artificial neural networks who’s algorithms can analyze millions of pictures of real people and places and use them to create convincing fictional ones.


B. who’s algorithms’
C. whose algorithm’s
D. whose algorithms


Who’s = who is, and you would not say …thanks to artificial neural networks who is algorithms can analyze millions of pictures. Rather, the possessive whose must be used. Whose algorithms = the algorithms of artificial neural networks. That eliminates (A) and (B). (C) is incorrect because algorithm’s is possessive, and a possessive noun can only be placed before another noun. The word following algorithms is can, which is a verb, and so no apostrophe should be used. The plural algorithms is thus correct, making (D) the answer.





The human eye may seem capable of taking in a lot of information, but in reality it can focus on only a thumbnail-sized area of vision—the brain fills in the rest. Furthermore, peripheral vision provides less details than central vision does, conveying images at a much lower resolution.


B. less details then
C. fewer details than
D. fewer details as


Less can only be used to modify singular, non-countable nouns. It would be acceptable to say less detail because detail is singular and cannot be counted, but details is plural and can be counted. Fewer must be used to modify plural nouns, making (C) and (D) the only possible options. In addition, the comparative (-er) form of an adjective must be paired with than, not as, eliminating (D) and making (C) correct.





When trying to learn new material, you might assume that the more work you put in, the better you will perform. Yet taking the occasional down time – to do literally nothing – may be exactly what you need. Dimming the lights, sitting back, and enjoying a few moments of quality contemplation will help one retain the information much more effectively.


B. us
C. you
D. them


To answer this question, it is necessary to consider the underlined pronoun in the context of the passage as a whole; the sentence in which that word appears does not provide enough information to answer the question. If you look back at the first two sentences, you can notice that they are addressed to you (you might assume, the more work you put in, may be exactly what you need). To keep the passage consistent, you must be used in the last sentence as well, making the answer (C).





Kagome baskets are characterized by a symmetrical pattern of interlaced triangles. A pattern that has preoccupied physicists for decades.


B. triangles, it is a pattern
C. triangles—a pattern
D. triangles; a pattern


The statement A pattern that has preoccupied physicists for decades is not a complete sentence because it is missing a main verb that corresponds to the subject. The verb has preoccupied “belongs” to the word that rather than to the subject, A pattern. Because it is not a sentence, it cannot follow a period or semicolon, eliminating both (A) and (D). (B) is incorrect because it contains a comma splice — two complete sentences separated by a comma (tip-off: comma + it). (C) correctly uses a single dash to create a single sentence broken into two parts and create a brief dramatic pause between those parts. Note that while a dash used this way must be preceded by a complete sentence, it can be followed by a fragment.


Looking for more practice? Check out the Quizzes and the Question of the Day Archives:





And for additional practice, Critical Reader Books include hundreds of practice questions and explanations.