Are Mr. and Mrs. Wang living alone in the house? —Yes, they have three sons, but ______ of them live in their own houses.

“How many students have visited the Summer Palace?”“.”

Last Sunday I had a good time _________volleyball with my frind Alan.

There great changes in Nanjing in the past few years. –I agree. And some more lines of the underground will be in service this year.

These young trees must ______.