Explanation
Correct answer: D.
Choice D is the best answer. The convention being tested is the use of verbs to express tense in a sentence. In this choice, the past progressive tense verb “was studying” is consistent with the other past tense verbs (e.g., “made” and “collected”) used to describe Buratti’s discovery. Further, the past progressive tense correctly indicates that an ongoing action in the past was occurring (she was studying) at the same time that another event occurred in the past (she made an interesting discovery).
Why the other choices are wrong
Choice A
Choice A is incorrect because the present tense verb “studies” isn’t consistent with the past tense verbs used to describe Buratti’s discovery.
Choice B
Choice B is incorrect because the present perfect progressive tense verb “has been studying” isn’t consistent with the past tense verbs used to describe Buratti’s discovery.
Choice C
Choice C is incorrect because the future tense verb “will study” isn’t consistent with the past tense verbs used to describe Buratti’s discovery.