— What's the population ____ the U.S.A?— The U.S.A has ____ population of 297 million.

 My father's ________ is my aunt. 

—I hear you run for half an hour every day. —Right, we have to. It is one of the ______ in our school.

There aren’t any___ between them.

I have some _________ in working out the problem.