OG详解-OG1 文法 Q8

Choice A is the best answer. The convention being tested is subject–verb agreement. The singular verb “allows” agrees in number with the singular subject “landing.”

Choice B is incorrect because the plural verb “are allowing” doesn’t agree in number with the singular subject “landing.” Choice C is incorrect because the plural verb “have allowed” doesn’t agree in number with the singular subject “landing.” Choice D is incorrect because the plural verb “allow” doesn’t agree in number with the singular subject “landing.”