The children looked up as the planes passed_____.

Universities generally （ ） their students from among the high school graduates.

My mother asked me where _____ the key.

_____ dictionary is enough for me.

（ ） the rain, we would have had a pleasant trip to the countryside.

He （ ） by his sister at that moment.

Have you checked all the CDs （ ） to the mountainous area next week?

It’s high time we _____ strict measures to stop pollution.

I have bought _____ useful reference books _____ I don’t know which one to start with.

He studies so hard to avoid （ ） at the bottom of the class.

Advertising is distinguished from other forms of communication （ ） the advertiser pays for the message to be delivered.

There was nothing we could do _____ wait at that moment.