Ⅰ.用所给动词的适当形式填空
1．Many new houses________(build)in the past few years.
答案 have been built
2．So far no letter________( receive) from my friends.
答案 has been received
3．The room_______ already _______(clean)，hasn't it?
答案 has; been cleaned
4．Such a thing ________ never been ________(hear)of before.
答案 has; heard
5．By the time you get to San Francisco tomorrow, I ________ (leave)for Southeast Asia.
答案 will have left
