주어진 글 다음에 올 글의 순서로 가장 적절한 것은? Neuroscientists and those in middle age or beyond know that brains alter and slow as we grow older. Processing speed, which is a measure of how rapidly our brains can absorb, assess and respond to new information, seems to be particularly hard hit. Most people who are older than about 40 perform worse on tests of processing speed than those who are younger, with the effects accelerating as the decades pass. (A) But in older people, brain scans show, the white matter can be skimpier and less efficient. Messages stutter and slow. (B) Scientists suspect that this decline is due in large part to a concomitant fraying of our brain's white matter, which is its wiring. (C) In young brains, these messages whip from neuron to neuron with boggling speed. (D) White matter consists of specialized cells and their offshoots that pass messages between neurons and from one part of the brain to another.