Mary didn’t understand           made her deskmate so upset all the morning.

It was in the village        he once lived        he got his junior education.

The question that puzzled us is _____ we can get rid of the air pollution in the area.

It was the building of the rail network from the west to the east coast ________ brought even larger numbers to California in the 1860s.

Was it when he returned        he was caught in a snowstorm?

—When did you meet him?
—It was on the day ____his house was broken into.

It was his courage, not his skill,    really struck me most

Sometimes I cannot but wonder ______ that has made me feel differently from the others.

In my opinion, all Mr. Li ______ good to his students in his class at present. He is very strict with them in their studies.

It was with great courage _______ the boy told the truth ______ he had stolen the money.