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: Social & Preventive Medicine
[{'content': 'Ohotolidine test is used for detecting which of the following? \nSelect and explain. \nA. Chlorine, B. Nitrites, C. Nitrates, D. Ammonia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ohotolidine test is used for determining both free and combined chlorine in water with speed and accuracy. Ref: Preventive and Social Medicine, By K.Park, 19th edition, Page 576, 578, 579, 582', 'role': 'assistant'}]