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': 'Indicator solution in Horrock’s Apparatus contains \nSelect and explain. \nA. Ortho-toulidine, B. Bromocresol purple, C. Ortho-toulidine arsenite, D. Starch iodide', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Indicator in Horrock’s apparatus: Starch iodide.\nIndicator in Presumptive coliform test (MPN Multiple Tube Method): Bromocresol purple.', 'role': 'assistant'}]