--- Listen! David is talking happily with his mother in the next room. --- It ______ be his mother. She has gone to Yunnan to be a volunteer doctor.
At present, the students in China take more exercise. Most of them are ______ than before.
—What a beautiful key ring! __________is it? —Only 5 yuan.
Jack will have a math test this afternoon. He needs a__________.
You are old enough to make decisions by __________.
There is __________backpack on the desk. It belongs to Tom.