Because a cycle of lunar phases ______ 29.5 days to complete, it’s possible to observe two full moons in a single month, one
at the beginning and one at the end.
are taking
have taken
take
takes
Choice D is the best answer. The convention being tested is subject-verb agreement. The singular verb "takes" agrees in
number with the singular subject "a cycle of lunar phases."
Choice A is incorrect because the plural verb "are taking" doesn’t agree in number with the singular subject "a cycle of lunar
phases." Choice B is incorrect because the plural verb "have taken" doesn’t agree in number with the singular subject "a cycle
of lunar phases." Choice C is incorrect because the plural verb "take" doesn’t agree in number with the singular subject "a
cycle of lunar phases."