– Have you decided how to spend your next day off?– Not yet. We ________ join the school volunteer project.A. may B. should C. must
—__________ 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.