he machine must be checked carefully before . A. using it B. used C. is used D.
来源：网络
时间：
推荐文章
he machine must be checked carefully before ______.
A. using it B. used C. is used D. being used
试题答案
D
before作介词用，后接动名词。
he machine must be checked carefully before ______.
A. using it B. used C. is used D. being used
D
before作介词用，后接动名词。