To survive when water is scarce, embryos inside African turquoise killiﬁsh eggs ______ a dormant state known as diapause.
In this state, embryonic development is paused for as long as two years—longer than the life span of an adult killiﬁsh.
enter
to enter
having entered
entering
Choice A is the best answer. The convention being tested is 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, “embryos”), and this choice supplies the clause with
the ﬁnite present tense verb “enter” to indicate how the embryos achieve diapause.
Choice B is incorrect because the nonﬁnite to-inﬁnitive “to enter” doesn’t supply the main clause with a ﬁnite verb. Choice C
is incorrect because the nonﬁnite participle “having entered” doesn’t supply the main clause with a ﬁnite verb. Choice D is
incorrect because the nonﬁnite participle “entering” doesn’t supply the main clause with a ﬁnite verb.