--- He’s already been back to Australia, _____ he?---_______________. He is on a visit to Shanghai.
What can we students do _____ the environment?
—How long have you lived in this town? —_____ 2001.
There are five people in the room, but I know _____.
Don’t give up _____ you will never succeed.
Trees can stop the sand _____ towards the rich farmland in the south.