<prompt> The active transport of Ca is regulated by ___ which is synthesized in kidneys:CholecalciferolErgosterol25-OH cholecalciferol1, 25-di OH-Cholecalciferol  <response>: Ans. D. 1, 25-di OH-Cholecalciferol1,25-DHCC is Vitamin D. It is synthesized in the body. The reactions takes place in the liver and kidney. Vitamin D is also known as a prohormone. It helps in the transport of calcium against the electrochemical gradient to promote mineralization of bones. 