--- ____ you _____ of the pop singer called Justin Bieber?--- Yes, I have. His voice sounds_____.
—__________ do I have to change the robot’s batteries? —Every two months.
Mr Chen __________ his mobile phone to the shop because it can’t work at all.
Computers have made a great difference _______ our everyday life.
After half a day’s hard work, we made our classroom look as _______ as new.
_______ provides many hours of air for astronauts in space.