This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'Role of liver in vitamin D metabolism \nSelect and explain. \nA. Catalyzes rate limiting steb, B. 1-hydroxylation, C. 25-hydroxylation, D. 24-hydroxylation', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Found in the liver, this enzyme is a microsomal vitamin D hydroxylase that conves vitamin D into 25-hydroxyvitamin D (calcidiol), which is the major circulatory form of the vitamin.', 'role': 'assistant'}]