Fact 1: Brain cells die quickly if their oxygen supply is cut off.

Fact 2: Blood carries oxygen to the brain.

Given the two facts above, answer the question "Brain cells die quickly if their what supply is cut off" with the following options: 
- energy
 - breathe
 - Energy.
 - alveoli
 - cut
 - CO 2
 - loss
 - blood


 

        blood 