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

下列各句中，没有语病、句意明确的一项是（）

4. It is _________ that you haven’t got the right answer. You have misunderstood our real intention.

The boss________company I worked in two years ago has________in solving such kind of problem

Hurry up, ____ you’ll be late

Thomas wants to know .