______ the average age of the population increases, there are more and more old people to care for.
Unless
Until
As
While
The government has taken some measures to solve the shortage of water, but it may be some time __ the situation improves.
— Why was it so noisy over there? — The Twins were surrounded by their fans ____ they stepped out of the hall.
Among the many dangers_________-- sailors have to face, probably the greatest of all is fog.
Mr. Black is willing to do ____________ Mrs.Black tells him to do.
_______ you are supposed to do is _______ it if you don’t like a thing. Don’t complain.