Which of the following is part of the urinary system?
a. liver
b. kidneys
c. stomach
d. gallbladder?

The liver doesn't really help out with the urinary system. The stomach, as you already know, is a part of the digestive system, where a lot of proteins are digested. The gallbladder is where your bile (a digestive "juice") is stored, so that has nothing to do with the urinary system as well.

Your kidneys, though, are a part of the urinary system, and that is where all the unwanted stuff in your blood is transferred to the urine.

Hope I helped!! xx