--- How _____ hours do you sleep a day?--- Well, about eight hours. But how _____ sleep do we students really need?

Only 16 percent of China’s area ____ covered with forests, so ____of us should protect trees. 

Not only the kids but also the teacher ________. We are worried because time is running out.

The number of people invited_______ fifty, but a number of them_______ absent for different reasons.

 ----A number of people_____ready to work in poorareas in the western part of China ----Yes,the number______getting________.