This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Physiology
[{'content': 'Type-2 pulmonary epithelial cells secrete \nSelect and explain. \nA. Surfactant, B. Mucus, C. Heparin, D. Polypeptides', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A', 'role': 'assistant'}]