Weixin（微信） chatting on the mobile phone by many people, and it’s very helpful.
A. is used for B. is used to
C. is used as D. is used by
—How many students are there in the classroom?
—_____ I don’t know where they have gone.
A.No one. B.None. C.Nobody. D.Nothing.
The rubbish _____ is produced every day is becoming a serious problem in cities around the world.
A. what B.that C.who D.whose
More and more trees were cut down. _____, many animals are dying out.
A.In the end B.So that C.As a result D.At last
We should often keep _____ touch with each other, because we are good friends.
A.on B.to C.in D.up
Everyone knows that a desk is made wood and paper is made wood, too.
A. of , of B. of , from C. from , from D from,of
