Answer:
I transfer oxygen from the atmosphere to your blood
you cannot keep me until you have given me
When you stop and look you can always see me. If you try to touch you cannot feel me. I cannot move but as you near me I will move away from you.
Whoever makes it, tells it not. Whoever takes it, knows it not. Whoever knows it, wants it not. What am I?
I have a head and a tail but my eyes can never see my tail.
It is something you make after you've weighed your options.