—Hi, Ethan. I called you at 8:00 last night, but you didn’t answer.
—Sorry, I ______ the dishes.
wash
washed
am washing
was washing
—__________ 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.