二、语态的选择

1. 被动语态，例：

Conservative philosophers argue that the very structure of society

by civil disobedience, while humanists stress the primacy of the individual conscience.

A) is threatening B) are threatening

C) is being threatened D) threatens

1. 为正确答案。本句应用被动语态，因为“社会结构（structure of society）”本身不可能发出“威胁”这个动作，它只能受到外界的威胁，注意后面“by 短语”的提示。

Experiments in the photography of moving objects in both the United States and Europe well before 1900.

1. have been conducting B) were conducting

C) had been condcted D) being conducted

1. 为正确答案。“实验”（experiments）只能被人做，故只能用被动语态， 符合此条件的只有（C），而 D）构成上有误。本句的时间状语为“before 1900”，因此从时态上说选 C），即应用过去完成时。

Orchestral instruments under the following types: strings, woodwind, brass, and percussion.

1. grouped B) can group

C) can be grouped D) to be grouped

C)为正确答案。判断主被动语态，关键要看主语能否发出谓语动词的动作。本句的主语“乐器”显然不能自己“组合”，故用被动态。

1. 主动语态，例：

Mild forms of exercise can some of the loss of flexiblity that accompanies aging.

A) stop B) to stop

C) stopping D) be stopped

A)为正确答案。和上例相同，主语“锻炼”本身也能起到“stop⋯flexibility” 的作用，故应选主动态。