You are presented with the question "Cell walls relax and increase the flow of what?" and the following answer choices: 
- heat
 - sugar
 - saliva
 - blood
 - oxygen
 - Air
 - semen
 - water

Now knowing that dilation occurs when cell walls relax and blood vessels dilate, the flow of blood to the skin increases and the muscles relax, choose the best answer.


 

    blood     