OG详解-OG4 文法 Q4

Choice D is the best answer. The convention being tested is subject-verb agreement. The singular verb “is” agrees in number with the singular subject “the triangle.”

Choice A is incorrect because the plural verb “are” doesn’t agree in number with the singular subject “the triangle.” Choice B is incorrect because the plural verb“have been” doesn’t agree in number with the singular subject “the triangle.” Choice C is incorrect because the plural verb “were” doesn’t agree in number with the singular subject “the triangle.”