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
Which of the following is used for Rickettsia ? 
Select and explain. 
A. Weil-Felix reaction, B. Rose-waler test, C. Poul-Bunnel test, D. VDRL
A: Weil-Felix reaction
Answer: A: Weil-Felix reaction 
Explanation: Ans. is 'a' i.e., Weil-Felix reaction