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: Physiology
[{'content': 'Human insulin differs from beef insulin by how many number of amino acid residues: \nSelect and explain. \nA. 1, B. 2, C. 3, D. 4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. 1', 'role': 'assistant'}]