This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Which vitamin is required for hydroxylation of proline? 
Select and explain. 
A. A, B. B, C. C, D. D
C: C
Answer: C: C 
Explanation: In Collagen Synthesis: Vitamin C is required for the post-translational modification, Hydroxylation of lysine and Proline Vitamin C plays the role of a coenzyme The hydroxylation reaction is catalysed by lysyl hydroxylase (for lysine) and prolyl hydroxylase (for proline) this reaction is dependent on vitamin C, molecular oxygen and alpha-ketoglutarate Hydroxyproline and hydroxylysine are essential for the collagen cross-linking and the strength of the fiber Ref: Satyanarayana 4th ed page 132