Antibiotics not being invented until the twentieth century, many ancient cultures used specially selected mold and plant extracts in order to treat infections.
(A) Antibiotics not being invented
(B) Antibiotics had not been invented
(C) While antibiotics had not been invented
(D) Although antibiotics have not been invented
(E) Although antibiotics were not invented
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Logical Relationship, Verb Tense
The two clauses in this sentence present opposing ideas, so a transition indicating that contrast is needed. That eliminates (A) and (B). (C) is incorrect because the past perfect (had + past participle) is used to refer to an event in the past that occurred before a second event in the past. In this case, however, the verb included in the underlined portion refers to a time (twentieth century) that clearly came after an earlier period (ancient cultures). (D) is incorrect because the present perfect (have + past participle) is used to refer to an action that is continuing into the present; however, the invention of antibiotics was a one-time occurrence that took place in the past. That leaves (E), which correctly uses the transition although to signal the contrasting relationship between the clauses and uses the simple past were to indicate a finished action in the past.