OG详解-OG3 文法 Q5

Choice A is the best answer. The convention being tested is subject-verb agreement. The singular verb “has enhanced” agrees in number with the singular subject “A Sheaf Gleaned in French Fields,” which is the title of a book of poems. 
Choice B is incorrect because the plural verb “are enhancing” doesn’t agree in number with the singular subject “A Sheaf Gleaned in French Fields.” Choice C is incorrect because the plural verb “have enhanced” doesn’t agree in number with the singular subject “A Sheaf Gleaned in French Fields.” Choice D is incorrect because the plural verb “enhance” doesn’t agree in number with the singular subject “A Sheaf Gleaned in French Fields.”