There was a tree in front of the house, ___ owner was seen sitting under it, enjoying the shade.

It was not until the teacher had explained it threetimes _______ how to work out the problem.

It is believed that a new kind of drug ______ by the scientists and they are hopeful that they will succeed in a few months

The audience ______ when they heard the humorousstory.

The boy likes to play tricks________the girls．So they don’t like him．