Which of the following are functions of the urinary system? 1. Vitamin D synthesis 2) Excretion 3) Regulation of red blood cell synthesis 4) Regulation of the concentration of solutes in the blood 5) Regulation of blood volume and pressure 6) Chemical digestion

A. 1, 2, 3, 4

B. 2, 3, 4

C. 1, 2, 3, 4, 5

D. 1, 2, 3, 4, 6

E. 2, 3, 4, 6