—Where is Mr. Wang? —He ______ Beijing on vacation.A. has been to B. has gone to C. went to
—__________ 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.