第20题: [单项选择]Passage Three Questions 32 to 35 are based on the passage you have just heard. A. Guarding the coasts of the United States B. Being part of the United States Navy. C. Guiding people along the coast. D. Protecting people from enemy attacks. 参考答案:A 答案解析:[听力原文]32-35 The Coast Guard does what its name says: it guards the coasts of the United State
第21题:[单选题]钠泵活动最重要的意义是 A.A:维持细胞内高钾 B.B:防止细胞肿胀 C.C:建立势能储备 D.D:消耗多余的 ATP E.E:维持细胞外高钙 参考答案:C