Choice D is the best answer. The previous question asks about the significance of Maguire's findings, with the answer being that her findings call into question a previous belief. This is supported in lines 20-26("neuroplasticity...true"): "It had long been thought that the adult brain was incapable of spawning new neurons—that . . . the brain's basic anatomical structure was more or less static. Maguire's study suggested the old inherited wisdom was simply not true."
Choices A, B, and C are incorrect because the lines cited do not support the answer to the previous question about the significance of Maguire's findings. Choices A and B are incorrect because these lines present Maguire's observation and her conclusion but do not indicate that her findings call into question a previous belief. Choice C is incorrect because these lines simply explain one capability of the human brain.