Good Riddles

Question: You wear me every day but you never put me on.
I will change colors if you leave me out too long.

What am I?

Question: What gets longer when pulled,fits between breasts, slides neatly into a hole,has choked people when used improperly,and works best when jerked?

Question: You find me behind the stars; or in a sixth, seventh, or third.
It takes something round, a computer, and me to make pie.
I am bigger than anything you can think of.

What am I?

Question: When is 1500 plus 20 and 1600 minus 40 the same thing?

Question: What is the only question you can't answer yes to?