If nephrons are the structural and functional units of the organs that manufacture urine, then nephrons are the structural and functional units of what?

Answer choices:
- 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       