OG5 阅读 Q50

Choice A is the best answer. After establishing in lines 50-51("difference ...those") that the brains of the control group and the mental athletes seemed to be "indistinguishable," the passage suggests that the reason mental athletes are so good at memorization is that they use parts of their brains that most other people don't use when memorizing: "Surprisingly, when the mental athletes were learning new information, they were engaging several regions of the brain known to be involved in two specific tasks: visual memory and spatial navigation, including the same right posterior hippocampal region that the London cabbies had enlarged with all their daily way-finding" (lines 66-72, "Surprisingly...first"). 
Choices B and C are incorrect because the passage explains that the mental athletes were converting information into images, not abstract symbols or numerical lists. Choice D is incorrect because it is not supported by the passage, as the author discusses the mental athletes' actions while memorizing but not any brain exercises the mental athletes regularly do.