问题

y possible means ______ to prevent the air pollution, but thesky is still not clear.

A:is used
B:are used
C:has been used
D:have been used

正确答案是：

同类题型

______ many students in China ever ______ to westerners before

The story is and all of us are in it.

Hello! Would you like to go to the partywith me tonight? –I’m sorry I can’t . Mother won’t ______meto go out in the evening.

Since you are new here, I’ll let Jack show you the community.

Instead of a letter, Tom made a telephone call to her mother.