Scientists have discovered amazingevidence showing how the human body rebuilds _______ while we sleep.

My classmates asked me ______ possible to improve their English in half a year.[ ]

In the opinion of many people, body-bombers are forced to do so but ______ many of them arewilling to.[ ]

Sometimes____turns off the lights in the classroom, because everybody thinks somebody will do it.

There are _____ reasons for the great changes in the countryside. [ ]