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 aging 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 sections of the brain, which relate to intellect (智能) and emotion, and determine the human character. (The rear section of the brain, which controls functions like eating and breathing, does not contract with age, and one can continue living without intellectual or emotional 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 remedy to the contraction normally associated 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 towns. 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 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.” On what are their research findings based ？（）

A survey of farmers in northern Japan.
B. Tests performed on a thousand old people.
C. The study of brain volumes of different people
D. The latest development of computer technology.