单项选择题

Making exercise a part of your daily life will do good to your heart. (1) , less than one-fifth of all adults get enough to appreciably improve their health. Exercise has specific heart (2) . When you exercise, you are helping to (3) your blood pressure and cholesterol (4) . Exercise can (5) reduce the blood’s tendency to clot—often a (6) of heart attacks. When major arteries are diseased, (7) even improves the blood supply (8) the heart. You don’t have to become a dedicated runner, jogger, or swimmer to (9) the benefits of exercise. The latest word (10) fitness experts is that small bouts of moderate exercise— (11) for a half hour to an hour, three or four times a week—is (12) you need. Brisk walkers had half the amount of heart disease deaths (13) those who did not walk for aerobic exercise, reports Dr. Steven Blair, head of a landmark study at the Institute for Aerobic Research in Dallas. "Your top fitness (14) is to try to work (15) about 2,000 calories a week through exercise," according to Dr. Blair. Run, jog, swim, play tennis (16) you must; these activities (17) off 500 to 600 calories an hour or so daily uses (18) 1,200 to 600 calories a week and will provide a big fitness boost. A brisk walk at four miles per hour will (19) 480 calories an hour. Ten minutes here, 10 minutes there, walking a few extra blocks, climbing stairs instead of taking the elevator will help (20) your heart in shape.

A.up
B.down
C.between
D.within
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