详解
Choice B is the best answer. The previous question asks what Maguire's study of mental athletes attempted to answer, with the answer being the question of whether it is brain structure or an unusual use of the brain that gives certain people extraordinary memorization skills. This is supported in lines 33-37("World ...possess."):"They wanted to find out if the memorizers' brains were—like the London cabbies'—structurally different from the rest of ours, or if they were somehow just making better use of memory abilities that we all possess."
Choices A, C, and D are incorrect because the lines cited do not support the answer to the previous question about what Maguire's study of mental athletes was investigating. Instead they simply identify the subject of the study (choice A), explain what the study involved (choice C), and state a finding concerning the cognitive ability of the mental athletes (choice D).