- Mr Li is said to be very patient with his students. - Yes. But it's really a hard_______ for him to control a class of young children.

These natural disasters have warned us that everyone should start to protect the _____ immediately.

Last night Jach worked for _________ after twelve o’clock..

The air pollution is very serious,we should take___________to stop it.

Mr. Green likes traveling. This summer he is going to Spain for    .