Growing population resulted in growing rubbish.—There is ______that rubbish will become the major threat to human beings in future.
We ________ get up early if there is _________ left.
___ nearly all behavior is learned behavior is a basic assumption of social scientists.
The house rent is expensive.I’ve got about half the space I had at home and I’m paying________here.
His father _____ to Nanjing. He _____ back next week.