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: Medicine
[{'content': "Severity of spreading of plague is detected by \nSelect and explain. \nA. Cheopis index, B. Total Flea index, C. Burrow's index, D. Chandler's index", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Cheopis index:- It is average number of X. Cheopis / rat.', 'role': 'assistant'}]