Working from an earlier discovery of Charpentier’s, chemists Emmanuelle Charpentier and Jennifer Doudna—winners of the
2020 Nobel Prize in Chemistry—re-created and then reprogrammed the so-called “genetic scissors” of a species of DNA-
cleaving bacteria ______ a tool that is revolutionizing the ﬁeld of gene technology.
to forge
forging
forged
and forging
Choice A is the best answer. The convention being tested is the use of ﬁnite and nonﬁnite verb forms within a sentence. The
nonﬁnite to-inﬁnitive “to forge” is correctly used to form a nonﬁnite (inﬁnitive) clause that explains why the chemists re-
created and reprogrammed the DNA-cleaving bacteria.
Choice B is incorrect. Without a comma separating the main clause (“chemists...bacteria”) from the participle “forging,” this
choice illogically suggests that the bacteria are forging a tool, which doesn’t make sense. Choice C is incorrect. Without a
coordinating conjunction such as “and” placed before it, the ﬁnite past tense verb “forged” can’t be used in this way to
describe the chemists’ actions. Choice D is incorrect. If read as a ﬁnite verb, the present progressive verb “forging” isn’t
consistent with the past tense verbs used in this sentence to describe the actions of the chemists. If read as a nonﬁnite verb,
the participle “forging” can’t be used in this way because there is no following main clause for it to modify.