A: _____is Mary?B: I think she is at home．

Peter, __________ do you visit your grandparents? –Twice a month.

There is _____ river at the foot of the mountain(山). _____ river is dangerous.

We get _______ sometimes when we study in a group. But we can learn from each other in this way.

Many birds are out of ____________ now, because we have done a lot of things to protect __________ birds.