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: Pharmacology
[{'content': 'The effect of morphine which has least tolerance is ? \nSelect and explain. \nA. Analgesis, B. Respiratory depression, C. Constipation, D. Bradycardia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]