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.
You 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 burn more fat than if you had 56 in a short burst of high-intensity exercise. In short, a brisk 30-minute walk will burn fat while a 100-yard sprint will burn glycogen.
[A] positive[B] additional[C] duration[D] effective [E] shed [F] physical
[G] food [H] functions [I] participated [J] rely [K] cut [L] repeatedly
[M] uses [N] little [O] obvious
47. E 该空需填入动词原形，结合原意“和大多数美国人一梯状，你(的体重)可能也有几磅需要________”可知，E(去除)最符合文意。
48. F 结合常识和下文可知，F最符合文意。
49. A 结合句意“令人惊奇的是，为了看到长期________效果你不必节食或常去健身馆”，可知空格处需填一形容词，初选后留下A、D。由于下文只是讲到运动会帮助减肥，但并未说明它的效果明显，所以此处宜选用意思上更宽泛的positive(正面的，有效的)。
50. H 下文举例的breathing, blood circulation and digestion都是人体的基本功能，且其后的functioning已给出了提示，故H最符合文意。
51. B 该空需填入形容词，结合常识和句意“任何时候只要你活动，你都需要________能量”来看选项，B(额外的)符合文意。
52. C 该句句意为“采用这两种能量消耗来源中的哪一种取决于你活动的强度和________”，结合下文提到的...low to moderately intense and of long duration...可知C最符合文意。
53. J 结合句意“(活动的)强度越低，身体越________于脂肪作为其燃料”，该空应填入能和on搭配的动词，J最符合文意。
54. D 结合常识可知，有氧运动是最有效的减肥方式，选项中D最符合文意。
55. L 该空需填入副词，选项中只有L和N可作副词，由下文提到的walking, running, swimming, dancing, and jumping等可推知在这些有氧运动中四肢的活动是反复的，故排除N。
56. I 该空需填入动词的过去分词，结合句意“如果你已经________高强度、爆发性的运动，你会燃烧更多的脂肪”可知I最符合文意。