—Did you meet Tom at the airport?—No.His plane________by the time I________there.
Liang Li always helps others _____ she is very busy.
None of us _____ running, but we all like swimming.
—Is _____ ready for the trip? —No, we haven’t got a camera.
The cleaners must keep the street _____.
We must plant more trees after we _____ every year.