The major storage and circulatory form of vitamin D is:-: (A) 25-hydroxycholecalciferol, (B) 1,25-dihydroxycholecalciferol, (C) Cholecalciferol, (D) Calcitriol
Answer is A. 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