The middle and high school period is a special one for children, a transition from children to adult, ______ children tend to be rebellious.
The traditional view is ____ we sleep because our brain is “programmed” to make us do so.
Then you usually lie there just ______ the ceiling, thinking about everything that could go wrong.
—What do you think of his opinion? —None has given me ___________ piece of advice.
The boy should be punished. You shouldn’t let him ______ cheating in the exam.
You can only be sure of _____ you have at present;you cannot be sure of something _____ you might get in the future.