—Do you know the mission of the volunteers?—No. But I think _____ they will end up doing there will promote public awareness of environmental protection.

______he has made up his mind, no one can make him change it.

Our government has taken some measures to overcome the lack of electricity, but it may take some time _____ we have enough power．

A lot of people don’t learn from their mistakes ______ they get hurt. 

This word can be used both as a noun ___ as a verb.