单项选择题
| The process of gaining or losing weight
can be explained by comparing your body to your car. Both run (56)
fuel, food for your body and gasoline for your car. Both (57)
that fuel, first into heat, then energy, some of (58)
is used to do work, and some emitted as waste. And (59)
your car uses more energy when the engine is racing than when it is
idling, (60) does your body use more energy when you are
working hard than (61) you are resting. For the purpose of this comparison, (62) , there is one significant difference between them. Your car cannot store fuel by turning it into (63) else; all gasoline not (64) remains as gasoline. But your body stores (65) energy as fat. When the gas tank is (66) empty, the car won’t run; but your body can burn fat to provide more energy. Therefore, if you want to gain weight, you must do (67) of two things: eat more calories (units of heat, therefore energy), or use less through (68) . If you want to lose weight, you do the (69) , decrease your intake of calories or increase the amount of energy you spend. There is (70) way. Gaining or losing weight is always a relation between intake and output of potential energy. |