33．When problems such as energy crisis, pollution and population explosion_________, people are asked to share the bitterness and endure the hardship with all the whole nation of the times．

He has lived ________ in a(an) _________ village since his wife died.

Since there’s no more work to do, we might just ________ go home

Look! Some of the children _____ in the river. —Oh, it’s dangerous to do that. We must _____ them.

It is dangerous to make the little boy ____ at home by himself.