You are presented with the quiz "What is a waste product of the body that is excreted by the urinary system?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "urine is the liquid waste product of the body that is excreted by the urinary system" and "mammals excrete urea in the watery form of urine ". 

So, what's the best answer to the question?


 

     urea      