This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: obstetrics,pediatrics and geriatrics, Subject name: Social & Preventive Medicine
[{'content': 'MMR is expressed as a rate per \nSelect and explain. \nA. 100 live bihs, B. 1000 live bihs, C. 10000 live bihs, D. 100000 live bihs', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ref:Park's Text book of Preventive and Social Medicine 25th ed", 'role': 'assistant'}]