In the 1970s, Janaki Ammal, a prominent botanist, emerged as a powerful voice in India’s environmental conservation
movement. Her exhaustive chromosomal survey of plants in Silent Valley, a pristine tropical forest in Kerala, India, that is
home to nearly 1,000 species of native ﬂora (many of which are endangered), ______ instrumental in the government’s
decision to preserve the forest.
are
were
have been
was
Choice D is the best answer. The subject "survey" is singular, and so is the verb "was."
Choice A is incorrect. The subject "survey" is singular, but the verb "are" is plural. Choice B is incorrect. The subject "survey" is
singular, but the verb "were" is plural. Choice C is incorrect. The subject "survey" is singular, but the verb "have been" is plural.