OG5 阅读 Q44

Choice D is the best answer. In line 24("cells...structure"), the passage discusses the "brain's basic anatomical structure." In this context, the word "basic" most nearly means fundamental. 
Choices A, B, and C are incorrect because in the context of discussing the brain's structure, the word "basic" most nearly means fundamental, not first (choice A), uncomplicated (choice B), or required (choice C).