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: Social & Preventive Medicine
[{'content': 'Crude birth rate is a simplest measure of fertility because it includes \nSelect and explain. \nA. Mid year population, B. Total population, C. Live births only, D. Pre-term births', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Crude birth rate : Number of live births in a year per 1000 mid-year population.\nCBR is simplest indicator of fertility : Total mid-year population is not exposed to child bearing thus it doesnot give true idea of fertility of a population.', 'role': 'assistant'}]