Mars, which was originally named after the Roman god of war, has been nicknamed the red planet because the iron oxide molecules prevalent on its surface gives them a reddish appearance.
(A) prevalent on its surface gives them a reddish appearance
(B) prevalent on their surface gives them a reddish appearance
(C) prevalent on its surface give it a reddish appearance
(D) prevailing on its surface give it a reddish appearance
(E) prevailing on its surface gives them a reddish appearance
Scroll down for the answer.
The answer choices contain various combinations of it(s) and them, a split that indicates that the question is testing pronoun agreement. The first pronoun must refer to Mars, singular, so its is correct. That eliminates (B). Now look at the second pronoun: iron oxide molecules prevalent on the surface of Mars give what a reddish appearance? Logically, this pronoun must refer to Mars, the “red planet,” as well – them would imply that iron oxide molecules give themselves a red appearance, a meaning that does not make sense. So the second pronoun is also singular, eliminating (A) and (E).
(D) is incorrect too because the standard adjective form of prevail is prevalent; the -ING form is awkward and unidiomatic.
(C) correctly includes prevalent as well as its/it.