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': "A farmer presenting with fever off-and on for the past 4 years was diagnosed to be suffering from chronic brucellosis. All of the following serological tests would be helpful in the diagnosis at this state except - \nSelect and explain. \nA. Standard Agglutination test, B. 2 Mercapto-ethanol test, C. Complement fixation test, D. Coomb's test", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]