OG详解-OG5 文法 Q3

Choice D is the best answer. The convention being tested is subject-verb agreement. The singular verb “ensures” agrees in number with the singular subject “using.”
Choice A is incorrect because the plural verb “are ensuring” doesn’t agree in number with the singular subject “using.” Choice B is incorrect because the plural verb “have ensured” doesn’t agree in number with the singular subject “using.” Choice C is incorrect because the plural verb “ensure” doesn’t agree in number with the singular subject “using.”