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': "To find out whether the water has been properly chlorinated, the test used is – \nSelect and explain. \nA. Horrock's test, B. Ortho–toludine test, C. Presumptive coliform test, D. Total bacterial count", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]