You are presented with the question "What does the process of urination require?" and the following answer choices: 
- aerobic capacity
 - relaxation of muscles
 - the looseness of soil
 - sunlight
 - air
 - metabolic reaction
 - blood
 - Converting waste.

Now knowing that urine leaves the body through a sphincter in the process of urination and urination requires relaxation of the sphincter muscle, choose the best answer.


 

  relaxation of muscles       