If you want to stay young,sit down and have a good think．This is

If you want to stay young,sit down and have a good think．This is the research result of professor Faulkner,who says that most of our brains are not getting enough exercise and as a result,we are ageing unnecessarily soon. Professor Faulkner wanted to find out why healthy farmers in northern Japan appeared to be losing their ability to think and to reason at a relatively early age,and how the process of ageing could be slowed down. He set about measuring brain volumes of a thousand people of different ages and occupations． Computer technology enabled him to obtain precise measurements of the volume of the front and side sections of the brain,which relate to intelligence and emotion,and determine the human character． Contraction of front and side parts--as cells die off--was observed in some subjects in their thirties,but it was still not evident in some sixty-and seventy-year-olds. Faulkner concluded from his tests that there is a simple way to slow the contraction—using the head. The findings show that contraction of the brain begins sooner in people in the country than in the towns．Those least at risk,says Faulkner,are lawyers,followed by university professors and doctors．White--collar workers doing routine work are,however,as likely to have shrinking brains as the farm worker,bus driver and shop assistant. Faulkner's findings show that thinking can prevent the brain from shrinking．Blood must circulate properly in the head to supply the fresh oxygen the brain cells need．"The best way to maintain good blood circulation is through using the brain,"he says．"Think hard and engage in conversation．Don't rely on pocket calculators." The professor's tests show that__.
A、our brains shrink as we grow old
B、the front section of the brain does not shrink
C、seventy-year-olds have better brains than sixty-year-olds
D、brain contraction may vary among people of the same age
【正确答案】：D
【题目解析】：根据文章的内容，我们可以逐一分析选项： A. 选项A提到“我们的大脑随着年龄增长而缩小”。虽然文章提到了大脑的某些部分可能会随着年龄的增长而缩小，但这并不是文章的主要结论。文章的主要焦点是如何通过思维活动来减缓大脑的缩小。 B. 选项B说“大脑的前部不会缩小”。这与文章中的信息相矛盾，因为文章明确提到了使用大脑可以减缓大脑前部和侧部的缩小。 C. 选项C表示“七十岁的人比六十岁的人有更好的大脑”。这同样与文章内容不符，文章没有比较不同年龄段人群的脑容量或大脑功能。 D. 选项D指出“同龄人之间的大脑缩小可能有所不同”。这是正确的。文章中提到，通过计算机技术测量的大脑体积显示，有些人在三十岁时就出现了大脑前部和侧部的缩小，但一些六十岁或七十岁的人却仍然没有明显的缩小。这证明了即使在相同年龄段，人们的大脑缩小程度也可能存在差异。 因此，根据文章内容，正确答案是D。