怠速时，变速器换入空档有响声，踩下离合器踏板下，响声消失，表明（）有故障。
A.变速器
B.离合器
C.变速器操纵机构
D.离合器操纵机构
参考答案：A
下列有关“一定”的说法中，正确的是（ ）
A．单质和化合物的反应一定是置换反应
B．纯净物一定是由同种分子构成
C．由同种元素组成的物质一定是单质
D．能分解出氧气的化合物一定是含氧化合物
Perhaps like most Americans you have some extra pounds to (47) . You may even have tried a fad diet or two, but found yourself right back where you started. The key to weight loss is regular (48) activity. And surprisingly, you don’t have to give up eating or make the gym your second home to see long-term, (49) effects.Your body needs a certain amount of energy to maintain basic (50) such as breathing, blood circulation and digestion. The energy required to keep your organs functioning is referred to as the resting or basal metabolic rate.Any time you are active, (51) energy is required. It is obtained from glycogen and fat stored in the blood, liver, and muscles. The key to losing weight is to draw on the fat rather than on the carbohydrate reserves.Which of the two energy sources you use depends on the intensity and (52) of your activity. The higher the intensity, the more your body will pull from the stored carbohydrates. The lower the intensity, the more your body will (53) on fat as its fuel.Aerobic exercise is most (54) for weight loss. When you perform aerobic activities you (55) contract large muscle groups such as your legs and arms. Walking, running, rollerblading, swimming, dancing, and jumping jacks are all forms of aerobic activity.Surprisingly, if your aerobic activity is low to moderately intense and of long duration, you will bum more fat than if you had (56) in a short burst of high-intensity exercise. In short, a brisk 30-minute walk will bum fat while a 100-yard sprint will bum glycogen.
