Answer:
Urinary system.
Step-by-step explanation:
The urinary system or the renal system involves kidneys, ureters, bladder and the urethra. Basically, the urinary system eliminates waste from the body, also regulates the volume, pressure, electrolytes and pH of the blood, that's why is the right answer here.
Therefore, the system that maintains the balance of fluids and minerals in the blood is the urinary system.