Fact 1: Urine leaves the body through a sphincter in the process of urination.

Fact 2: Fluids in the urine eliminate metabolic waste products.

Given the two facts above, answer the question "Metabolic waste products can leave the body through" with the following options: 
- burning coal
 - animal transport
 - Dehydration
 - radiative transfer
 - osmosis
 - convection
 - fossil fuels
 - a sphincter


 

        a sphincter 