I can’t remember _____ I put the book, and I need it for my homework now.
He’s been to the Great Wall,?
We believe scientists will a way to solve the problem of air pollution.
You had better _____ home at once . Don’t keep your mother _____ .
Remember ______ the book in time when you have finished _____ it .
It willabout half an hour to get to the zoo by bus.