第3题: [单项选择]We all write ______, even when there's not much to say. A. now and then B. by and by C. step by step D. more or less 参考答案:A 答案解析:[精解] now and then“时而,不时”。句意为“即使我们没有多少东西可说,我们都时不时写点什么。”by and by意为“渐渐地”;step by step意为“一步步地”;more or
第5题: [多项选择]通常认为是无效成分或是杂质的是() A. 皂苷类 B. 树脂类 C. 萜类 D. 氨基酸类 E. 油脂 参考答案:B, D, E
第6题: [单项选择]The passage is mainly concerned with the ______. A. geographical distribution of plant and animal species B. location and purpose of the pulvini C. appearance of the mimosa D. process that causes movement in the mimosa 参考答案:D 答案解析:[注释] 本文讲述的是含羞草植物枝叶运动的过程。