问题

The city park will be cleaner ___________ people stopdropping litter here and there.

A:while
B:if
C:unless
D:before

正确答案是：

同类题型

_____ have you lived there —Since 1970.

The music by Jay Chow_______ nice. I guess his CDs must_______ well.— Yes, he is very popular among young people.

The newcomer went to the library theother day and searched for ________ he could find about Mark Twain.

My brother plays ______ basketball well but he doesn’t play _______ piano well.

Please tell Tom football in the street．It’s dangerous．