考点：考查词组

点评：本题考查了副词down，up和不同的动词构成的短语，要注意一词多义的现象。重要的是别忽略了句意。

4.When I entered the step-classroom(阶梯教室), the lecture _________ and the people _________ attentively.

A. began, listened B. was begun, was listening

C. had begun, listened D. had begun, were listening

【答案】D

【解析】

【详解】考查时态。句意：当我走进阶梯教室时，讲座已经开始了，人们正在聚精会神地听着。根据entered，可知 "我走进阶梯教室时"这个动作发生在过去，而"讲座已经开始了"这个动作发生在过去的过去，所以第一个空用过去完成时；第二个空表示过去的某一时间，正在发生的动作，用过去进行时，故选D。

5.People can unlock the shared bikes, _________are equipped with GPS and can be left anywhere in public, by simply _________their smart phones.

A. which; use B. which; using

C. of which; use D. of which; using

【答案】B

【解析】

【详解】考查非限制性定语从句和动名词，句意：仅凭自己的智能手机人们能够解锁共享单车，这些共享单车配备了全球定位系统，可以被放在公共场合的任何地方。" are equipped with GPS and can be left anywhere in public"为非限制性定语从句，先行词为the shared bikes，指物，且先行词在从句中做主语，故用which指代。第二个空位于介词by的后面，用use动名词的形式做宾语，填using。综上，选B。

6._________ more and more forests damaged, some animals and plants are facing the danger of dying out.

A. As B. For

C. With D. By

【答案】C

【解析】