Answer:
By Moon or by Sun, I shall be found. Yet, if there's no light around, I am undone. What am I?
I transfer oxygen from the atmosphere to your blood
You use me from your head to your toes. The more I work, the thinner I grow. What am I?
My teeth help me suck.
When I get closer my tail grows longer but when I go away my tail leads the way.
What is yours but only used by others?