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 該空需填入動(dòng)詞原形，結(jié)合原意“和大多數(shù)美國人一梯狀，你(的體重)可能也有幾磅需要________”可知，E(去除)最符合文意。

　　48. F 結(jié)合常識和下文可知，F(xiàn)最符合文意。

　　49. A 結(jié)合句意“令人驚奇的是，為了看到長期________效果你不必節(jié)食或常去健身館”，可知空格處需填一形容詞，初選后留下A、D。由于下文只是講到運(yùn)動(dòng)會幫助減肥，但并未說明它的效果明顯，所以此處宜選用意思上更寬泛的positive(正面的，有效的)。

　　50. H 下文舉例的breathing, blood circulation and digestion都是人體的基本功能，且其后的functioning已給出了提示，故H最符合文意。

　　51. B 該空需填入形容詞，結(jié)合常識和句意“任何時(shí)候只要你活動(dòng)，你都需要________能量”來看選項(xiàng)，B(額外的)符合文意。

　　52. C 該句句意為“采用這兩種能量消耗來源中的哪一種取決于你活動(dòng)的強(qiáng)度和________”，結(jié)合下文提到的...low to moderately intense and of long duration...可知C最符合文意。

　　53. J 結(jié)合句意“(活動(dòng)的)強(qiáng)度越低，身體越________于脂肪作為其燃料”，該空應(yīng)填入能和on搭配的動(dòng)詞，J最符合文意。

　　54. D 結(jié)合常識可知，有氧運(yùn)動(dòng)是最有效的減肥方式，選項(xiàng)中D最符合文意。

　　55. L 該空需填入副詞，選項(xiàng)中只有L和N可作副詞，由下文提到的walking, running, swimming, dancing, and jumping等可推知在這些有氧運(yùn)動(dòng)中四肢的活動(dòng)是反復(fù)的，故排除N。

　　56. I 該空需填入動(dòng)詞的過去分詞，結(jié)合句意“如果你已經(jīng)________高強(qiáng)度、爆發(fā)性的運(yùn)動(dòng)，你會燃燒更多的脂肪”可知I最符合文意。