OG详解-OG5 文法 Q5

Choice D is the best answer. The convention being tested is subject-verb agreement. The plural verb “represent” agrees in number with the plural subject “references.”
Choice A is incorrect because the singular verb “represents” doesn’t agree in number with the plural subject “references.” Choice B is incorrect because the singular verb “has represented” doesn’t agree in number with the plural subject “references.” Choice C is incorrect because the singular verb “was representing” doesn’t agree in number with the plural subject “references.”