The room is big enough for us _________ .

Don’t forget      the lights when you leave.

At present, more and more people prefer _________ in the countryside because there is _____ pollution in the city.

 — My computer has gone wrong. It needs _______ soon. — Why not have David _______ it? Nobody can if he can’t.

---How did you work out the difficult chemistry problem?--- I worked it out by ________.