__________,they provide a rapid means of getting information about many people.A.Properly be used B.Properly used C.If u

问题描述:

__________,they provide a rapid means of getting information about many people.A.Properly be used    B.Properly used    C.If use it properly    D.Been properly used    原因要讲清楚

选c.这里面省略了主语They,因为后面有they,所以可以省略.然而一个句子不能有两个动词,所以A不选.B中把他省略的东西补上就是It is properly used.主语是it 与后面的主语不一样,不能省.没有D这种用法