Question

Computers are very useful in our lives, but they must        properly.
A. use                 B. be using                C. be used

Answer 1

C

試題分析：句意：電腦在我們的生活中非常有用，但是必須恰當地使用它們。結合語境可知下文主語是動作對象，故用被動語態，選C。