This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'Indicator solution in Horrocks apparatus contains \nSelect and explain. \nA. Oho toludine, B. Starch iodide, C. Ohotoludine arsenite, D. Bromocresol purple', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Horrock&;s apparatus is designed to find out the dose of bleaching powder required for disinfection of water.Starch-iodide indicator solution is used.Park 23e pg: 728', 'role': 'assistant'}]