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
[{'content': 'Richest source of retinoids is? \nSelect and explain. \nA. Cod liver oil, B. Halibut liver oil, C. Butter, D. Margarine', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. (b) Halibut liver oilRef: Harper's Biochemistry 27/e, chapter 44, Textbook of medical biochemistry S. Ramakrishnan 3/e, p 393", 'role': 'assistant'}]