This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
Active from of vitamin D is: 
Select and explain. 
A. Cholecalciferol, B. 24, 25 (OH) 2 Vit-D, C. 1, 25 (OH) 2 Vit-D, D. 25-OH Vit-D
C: 1, 25 (OH) 2 Vit-D
Answer: C: 1, 25 (OH) 2 Vit-D 
Explanation: Ans. (c) 1, 25 (OH) 2 Vit-D(Ref: Ganong, 25th ed/p.377)The active form of vitamin D is called 1, 25- dihydroxycholecalciferol or calcitriol