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: Unknown
[{'content': "Nichol's strain is used in: \nSelect and explain. \nA. TP HA test, B. TPI test, C. VDRL, D. FTA-ABS", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Treponema pallidum immobilization (TPI) test, considered both as a qualitative and as a quantitative test, and then various specific aspects of passage of the Nichols strain of treponeme in rabbit testes. a serological test for syphilis in which a solution containing the living causative spirochete (Treponema pallidum) is combined with serum in the presence of complement with immobilization of the active spirochetes indicating a positive result', 'role': 'assistant'}]