OG详解-OG1 文法 Q7

Choice B is the best answer. The convention being tested is pronoun-antecedent agreement. The plural reflexive pronoun “themselves” agrees in number with the plural antecedent “turtle barnacles,” correctly indicating what is attached to a sea turtle shell.

Choice A is incorrect because the singular pronoun “it” doesn’t agree in number with the plural antecedent “turtle barnacles.” Choice C is incorrect because it results in an unclear and confusing sentence. In this context, it’s unclear what the plural pronoun “them” refers to. Choice D is incorrect because the singular reflexive pronoun “itself” doesn’t agree in number with the plural antecedent “turtle barnacles.”