是表示"人口的百分之几、几分之几"时，谓语动词用复数形式。German的复数形式为Germans。reduce，rise等词后跟by表示变化幅度，后跟to表示达到的程度。故选A项。

4．...，volunteers were required not to eat or drink for eight hours before the experiment.......，志愿者们被要求在试验开始前八个小时内不吃不喝。

(1)volunteer n．志愿者；vt.& vi.自愿做，义务做

volunteer sth.自愿提供......，自愿给予......

volunteer to do sth.自愿做某事

volunteer for自愿参加

volunteer as/to be自愿成为......

(2)voluntary adj.志愿的；自愿的，主动的

(1)She volunteered some information.

她主动提供了一些信息。

(2)When she retired，she did a lot of voluntary work for the Red Cross.

她退休后为红十字会做了大量的志愿工作。

(3)Two men volunteered to search for the missing climber.

两个人自告奋勇地去寻找那位失踪的登山者。

[单项填空]

(4)Last week，my kids along with other kids from the neighbourhood to help me wash my car.

A．commanded B．contributed

C．preferred D．volunteered

答案　D

解析　句意为：上周，我的孩子们和邻居家的孩子们自愿帮我洗车。command要求；contribute贡献；prefer更喜欢；volunteer自愿。根据句意，故选D项。

5．One explanation is that women's sense of smell is better developed than that of men，and is linked to recognizing the smell of babies.

一种解释是女性的嗅觉比男性的发达，而且这和识别婴儿的体味有关系。