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: Microbiology
[{'content': 'The diagnostic test for rickettsial infection is: \nSelect and explain. \nA. Weil-felix reaction, B. WIDAL, C. Sabin test, D. Culture', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Weil-felix reaction', 'role': 'assistant'}]