题目内容：

It is said that if you want to stay young, sit down and have a good think. This is the research finding of a team of Japanese doctors, who say that most of our brains are not getting enough exercise — and as a result, we are growing old unnecessarily soon.

Professor Taiju Matsuzawa wanted to find out why otherwise healthy farmers in northern Japan appeared to be losing their ability to think and reason at a relatively early age, and how the process of aging could be slowed down. With a team of colleagues at Tokyo National University, he set about measuring brain volumes of a thousand people of different ages and varying occupations. Computer technology enabled the researchers to obtain precise measurements of the volume of the front and side parts of the brain, which controls functions like eating and breathing, does not contract with age, and one can continue living without intellectual on economical faculties. 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. Matsuzawa concluded from his tests that there is a simple way to the contraction normally connected with age — using the head.

The findings show in general terms that contraction of the brain begins sooner in people in the country than in the town. Those least at risk, says Matsuzawa, are lawyers, followed by university professors and doctors. White collar workers doing routine work in government offices are, however, as likely to have shrinking (萎缩) brains as the farm worker, bus driver and shop assistant.

Matsuzawa'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.”

1.The team of doctors wanted to find out ______.

A. the size of certain people's brains

B. how to make people live longer

C. which people are most intelligent

D. why certain people are aging sooner than others.

2.On what are their research findings based?

A. The study of brain volumes of different people.

B. The study of brain volumes of old people.

C. The latest development of computer technology.

D. A survey of farmers in northern old people.

3.The doctors’ tests show that _______.

A. our brains shrink as we grow older

B. the front section of the brain does not shrink

C. sixty-year-olds have better brains than thirty-year-olds

D. some people's brains have contracted more than other people's

4.According to the passage, which people seem to age more slowly than the others?

A. Lawyers.    B. Farmers.

C. Clerks.    D. Shop assistants.