This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The major storage and circulatory form of vitamin D is:- 
Select and explain. 
A. 25-hydroxycholecalciferol, B. 1,25-dihydroxycholecalciferol, C. Cholecalciferol, D. Calcitriol
A: 25-hydroxycholecalciferol
Answer: A: 25-hydroxycholecalciferol 
Explanation: Cholecalciferol is first hydroxylated at 25th position to 25-hydroxycholecalciferol (25-OH o3) bv a specific hydroxylase present in  liver. 25-OH D3 is the major storage and circulatory form of vitamin D.
Reference: Satyanarayana- Biochemistry, 3rd edition, pg-125