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: Social & Preventive Medicine
[{'content': 'Richest source of vitamin D is: September 2003 \nSelect and explain. \nA. Fish, B. Soyabean, C. Halibut liver oil, D. Vegetables', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. C i.e. Halibut liver', 'role': 'assistant'}]