Answer:
Where humans breathe liquid.
What is it that given one, you'll have either two or none?
What starts with an "e" but only has a single letter in it?
There is a man in a 4 story building. He jumps out of the window and is unharmed. He used no padding, and had no harm done. How?
What is the end of everything?
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.