题目内容：

选哪个,请给出原因.A.used B.has been used C.using D.is using
The computer,now______by millions of people,has changed the world

优质解答

A.used
now__used__by millions of people是个从句.被许多人使用.后面
The computer has changed the world,这是主句干.
所以now后面不能有谓语动词.故排除B和D.
因为是人用电脑.,所以用被动语态.所以答案是A