Experts say ________ to sunlight for too much time will do harm to one’s skin.
For centuries the upper classes in Britain spoke French ______ the common people spoke English.
As a matter of fact, it was the third time that we ______ your school.
--- There's going to be a concert this evening and we want to go there very much.--- The question is ______ we can get a couple of tickets.
People who are addicted ______ drugs cannot go without them for a few hours.
It is said that our school is ______ 72 classes, not including international classes.