Answer:
What is that which, though black itself, enlightens the world without burning?
I can be written, I can be spoken, I can be exposed, I can be broken.
When I get closer my tail grows longer, but when I go away my tail leads the way.
What goes in, but never through? I've got some and so do you. We might lend one, or even two, but only if our trust is true.
I bind it and it walks. I loose it and it stops.
A red house is made out of red bricks. A blue house is made out of blue bricks. What is a green house made out of?