Identify the Role of the Urinary System in Acid ^-base

Identify the role of the urinary system in acid ^-base balance. 1. The kidneys can secrete bicarbonate ions when the pH of the blood rises.
2) The kidneys contribute to acid ^-base balance by excreting fixed acids that the lungs cannot excrete.
3) The kidneys can manufacture new bicarbonate ions when the pH of the blood falls.
4) The kidneys contribute to acid ^-base balance by controlling the concentration of bicarbonate ions in the blood.

A) 1, 2, 3, 4
B) 2, 3, 4, but not 1
C) 1, 3, 4, but not 2
D) 1, 2, 3, but not 4