______ the average age of the population increases, there are more and more old people to care for.
Unless
Until
As
While
So mysteriously ______ missing that many puzzles wait to be solved.
For a moment nothing happened, and then ______ all shouting together.
---I have finished my homework. ---___________.Let’s go to play tennis.
— Did you know any French before you arrived in Washington? — Never ______ it, actually.
Only after her mother came to help her for the first few months _____ to begin her propjet.