单项选择题

Jogging has become most popular in America. Many theories have been raised to explain its (36) . The plain truth is that jogging is (37) , quick and efficient to (38) physical fitness.
The most useful sort of exercise is exercise that (39) the heart, lungs, and circulatory system. If these systems are (40) , the body is ready for almost any sport and for almost any sudden (41) . One can train more specifically, (42) by developing strength for weight lifting (43) the ability to run straight ahead (44) short distances with great power as in football, (45) running trains your heart and lungs to deliver oxygen more efficiently (46) all parts of your body. It is (47) noting that this sort of exercise is the only kind that can (48) heart disease, which is the number one (49) of death in America.
(50) one sort of equipment is needed—a (51) of good shoes. Physicians (52) beginning joggers not to try to run in a tennis or gym shoe. Many design (53) have been made in the last several years. These make an excellent running shoe (54) if a runner wishes to develop as quickly as possible, with (55) little chance of injury as possible.

36().

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