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': 'Usually healthy human volunteers are taken in: \nSelect and explain. \nA. Phase I of clinical trial, B. Phase II of clinical trial, C. Phase III of clinical trial, D. Phase IV of clinical trial', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]