Fact 1: Dilation occurs when cell walls relax.

Fact 2: Blood vessels dilate, the flow of blood to the skin increases and the muscles relax.

Given the two facts above, answer the question "Cell walls relax and increase the flow of what?" with the following options: 
- heat
 - sugar
 - saliva
 - blood
 - oxygen
 - Air
 - semen
 - water


 

    blood     