We all age at different rates. Heredity clearly plays an important part. But recent resear

ch studies by gerontologists indicate that life-style. may be equally significant in determining who will remain youthful.

As a rule, single men and women have shorter lives than married men and women. Studies show that those who have been widowed, especially men, have a longer life expectancy if they remarry soon. Both men and women seem to have a greater resistance to disease and death when their marriage is undamaged. According to a 1960 study, women who have borne three children have the lowest mortality rates. Those who have borne four or more have the highest. Childless women and those with only one child generally don't live as long as mother of two or three, according to University of Chicago sociologists Evenly M. Kitagawa and Philip M. Hauser.

It's impossible to say how much sleep is ideal. Some people thrive on five hours a night, others seem to require eight or nine. Scientists agree that consistency in sleeping pattern is more significant; it's better to get six hours' sleep every night than ten hours one night and three the next.

While it's true that very few people who enjoy a long life are fat, this does not mean that every pound you gain is going to shorten your life. In fact, an ongoing study in Framingham, Mass. , has showed that during at least 30 years of middle life, leanness was a higher factor for mortality than fatness! What is known is that weight extremes in either direction are definitely unhealthy. Weighing 20 percent more or less than you should weigh can, in certain cases, be a life shortener.

The benefits of regular exercise are indisputable. Men engaged in energetic and persistent physical labor have fewer heart attacks. But many researchers believe that exercise need not be very strong to keep you in shape. The first principle of any life-extension program, then, is to enjoy every moment of the life you have—whether it lasts one more year or a hundred. As the philosopher Jean Jacques Rousseau put it: "Teach him to live rather than to avoid death. Life is not breath but action, the use of our senses, mind, faculties, every part of ourselves which makes us conscious of our being. "

Which of the following is not beneficial to the lengthening of life？

A．You should keep a good sleep habit.

B．You should do physical exercise on a regular basis.

C．You should try and remain neither too lean nor too fat.

D．You should take part in a guided life-extension program.