Experts are trying to work out a plan to deal with the problems caused by global warming ______ it is too late.

When I talked about the thing, I felt Jane watching me uncomfortably，looking____ she wished to speak.

I was about to leave _____ the telephone rang.

When the last prize had been awarded _________ everybody cleared off. 

The government has taken some measures to solve the shortage of electricity , but it may be some time _________the situation improves.