Heavysmog (雾霾 )ineastern and central China seemsto get more and more serious. —I agree. Something todeal with it.

Can you tell the ________ difference between the words “require” and “request”? I sometimes get puzzled by their meanings.

166. I think your bookshelf is too high. I can’t reach a book on top even when I _____ my hand.

The problem ________ this material can beused in our factory has been solved.

The students were sitting in the classroom with their eyes on the teachers.