Fact 1: Nephrons are the structural and functional units of the kidneys.

Fact 2: Normally the kidneys manufacture urine.

Given the two facts above, answer the question "nephrons are the structural and functional units of what?" with the following options: 
- Something coming from a gland
 - A compound that donates proton
 - urine manufacturing organs
 - Veins and arteries.
 - critical organs
 - sensory neurons
 - food and shelter
 - the body's largest organ


 

   urine manufacturing organs      