To survive when water is scarce, embryos inside African turquoise killifish eggs blank 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.
Which choice completes the text so that it conforms to the conventions of Standard English?
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.