When did you last see a polar bear? On a trip to a zoo, perhaps? If you had attended a w

　　When did you last see a polar bear? On a trip to a zoo, perhaps? If you had attended a winter activity in New York a few years ago, you would have seen a whole polar bear club. These Polar Bears are people who meet frequently in the winter to swim in freezing cold water. That day, the air temperature was 3℃, and the water temperature was a bit higher. The members of the Polar Bear Club at Coney Island, New York are usually about the age of 60. Members must satisfy two requirements. First, they must get along well with everyone else in the group, this is very important because there are so many different kinds of people in the club. Polar Bears must also agree to swim outdoors at least twice a month from November through February.
　　Doctors do not agree about the medical effects of cold-water swimming. Some are worried about the dangers of a condition in which the body's temperature drops so low that finally the heart stops. Other doctors, however, point out that there is more danger of a heart attack during summer swimming because the difference between the air temperature and water temperature is much greater in summer than in winter.
The Polar Bears themselves are satisfied with the benefits (or advantages) of cold-water swimming. They say that their favorite form of exercise is very good for the circulatory system(循环系统) because it forces the blood to move fast to keep the body warm. Cold-water swimmers usually turn bright red after a few minutes in the water. A person who turns blue probably has a very poor circulatory system and should not try cold-water swimming.
　　The main benefits(or advantages) of cold-water swimming are probably mental. The Polar Bears love to swim year-round; they find it fun and relaxing. As one 70-year-old woman says. When I go into the water, I pour my troubles into the ocean and let them float away.
51. The members of the Polar Bear Club must meet the following requirements except that     .
　A. they should be easy to make friends with
　B. they must swim outdoors at least 8 times in the four cold months
　C. they must agree to swim outdoors from November through February
　D. they must reach the age of 60
52. Doctors      .
　A. encourage people to take part in cold-water swimming actively
　B. point out the possible danger of blood illness during cold-water swimming
　C. believe swimming is helpful both in winter and in summer
　D. have different ideas about the medical effects of cold-water swimming
53. According to the passage, some doctors believe it is true that      .
　A. you are healthy if cold-water swimming turns your skin color blue
　B. cold-water swimming causes more heart attacks in summer than in winter
　C. cold-water swimming can make the body temperature dangerously high
　D. Polar Bears are bears swimming in freezing water
54. The Polar Bears like to swim all the year round, for      .
　A. they can remain young   B. it is an easy way to keep the body warm in winter
　C. they find it enjoyable and interesting D. they might meet fewer troubles in life
55. The passage is mainly about      .
a group of cold-water swimming lovers                  B. the polar bears' life  
　C. doctors' ideas about cold-water swimming            D. the requirements of the Polar Bear Club51－55 D D B C A