The scientists, who were formerly physicists, always claimed the most vital _________ was how to question established theories.
Which choice completes the text so that it conforms to the conventions of Standard English?
thing they mentor taught
his mentor taught their mentor taught them
their mentor taught them
they mentor taught them
Correct Answer: C
Choice C is the best answer. The sentence refers to "The scientists" (plural). The correct possessive pronoun to refer to them is "their." The phrase "their mentor taught them" completes the thought logically.
Choice A is incorrect because "they" is a subject pronoun, not a possessive adjective. Choice B is incorrect because it is redundant and syntactically confusing. Choice D is incorrect because "they" is a subject pronoun used incorrectly in place of a possessive.