Choice A is the best answer. The second sentence of the sixth paragraph states: "Students who have trouble remembering distinct facts, for example, may struggle to employ those facts in critical thinking." In other words, students who find it difficult to remember information may find it challenging to utilize that information to develop logical arguments. Therefore, the word "employ," as used in the context of this sentence, most nearly means utilize.
Choices B, C, and D are incorrect because in the context of the passage, "employ" means utilize, not enroll (choice B), exert (choice C), or assign (choice D).