______ the average age of the population increases, there are more and more old people to care for.
Unless
Until
As
While
—Do you need the electric dryer?—________.
—Why are you moving out?—________, but I just don't like the atmosphere here.
—Believe it or not, I have met him before.—No kidding? ________ you've never mentioned it?
—What's the capital of Bhutan?—________ Let's go online and find it out.
—I hear Kris had an accident as he was riding his bike to school yesterday.—________? He is always so careful when he is riding.