单选题 Rope skipping has many advantages for someone looking for an inexpensive and convenient form of exercise. It (51) to all the components of physical fitness, (52) in the area of cardiorespiratory(心和肺的)endurance. Rope skipping can be done (53) or in pairs. The ends of the rope are held loosely in the fingers. Elbows should be (54) the sides and the arms pointed away from the body. The arms and shoulders move in circular motion; as the rope follows a circular motion, (55) momentum (力量，势头)can be provided by rotating the wrists. (56) by pushing off from the toes just (57) enough to allow the rope to pass under your feet.
Some physical educators (58) that rope skipping expends as much energy as running. Another (59) is the relatively short time it takes to perform the activity. Some people rope skip for 10 minutes and feel that this is (60) to jogging for 30 minutes, at least (61) terms of energy expenditure (消耗). An added advantage of rope skipping (62) an activity for many students is that they do not have to skip on hard surfaces. Some students find jogging difficult because of the need to (63) on hard surfaces. Rope skipping, on the other hand, (64) be performed indoors or outdoors on a hard or (65) surface. Rope skip- ping can be done almost anywhere at anytime, providing there is space enough for the rope to make a complete revolution.