Pollution is a serious problem. Scientists have _______ some good ways to save it.

―Thank you very much for giving me a hand when I was in trouble.―Don’t mention it. I only did what anyone else _______ in my place.

You can’t imagine what difficulty we had_______ home in the snowstorm.

The number of smokers in China ________increased in recent years, and a number of them _________ the youth.

what their friendships are based upon, the important thing toremember is bothof them are friendships.