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': 'Which of the following casein predominates in cow milk: \nSelect and explain. \nA. a casein, B. b casein, C. Equally present, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: a casein predominates in cow milk, whereas b casein predominates in human milk and the former may act as an allergen. Ref:Nutrition and Child Development, K.E. Elizabeth, 4th edition pg: 17', 'role': 'assistant'}]