Even though bats prefer very sweet nectar, the plants that attract them have evolved to produce nectar that is only
moderately sweet. A recent study ______ why: making sugar is energy-intensive, and it is more advantageous for plants to
make a large amount of low-sugar nectar than a small amount of high-sugar nectar.
explains
explaining
having explained
to explain
Choice A is the best answer. The convention being tested is the use of ﬁnite and nonﬁnite verb forms within a sentence. A
main clause requires a ﬁnite verb to perform the action of the subject (in this case, “a recent study”), and this choice supplies
the ﬁnite present tense verb “explains” to indicate that the study explains why plants that attract bats have evolved to
produce moderately sweet nectar. 
Choice B is incorrect because the nonﬁnite participle “explaining” doesn’t supply the main clause with a ﬁnite verb. Choice C
is incorrect because the nonﬁnite participle “having explained” doesn’t supply the main clause with a ﬁnite verb. Choice D is
incorrect because the nonﬁnite to-inﬁnitive “to explain” doesn’t supply the main clause with a ﬁnite verb.