You are presented with the question "What causes cell walls to relax?" and the following answer choices: 
- exercise
 - sweating
 - adding heat
 - Energy
 - dilation
 - heat or cold
 - heat
 - Dehydration

Now knowing that dilation occurs when cell walls relax and when oxygen level decreases, dilatation of the blood vessels occurs, choose the best answer.


 

     dilation    