There is no doubt      one who gets to the finishing line first will win the first prize.

—What about your TEFL test? —I have answered all the questions, but I’m not sure _____ I could get a high enough score. 

____ has finished the work ahead of time will be rewarded though we don't know who it will be.

Is it high time that the children _____ go to school ?

___is certain is ___prevention is more important than treatment .