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
Indicator solution in Horrock’s Apparatus contains 
Select and explain. 
A. Ortho-toulidine, B. Bromocresol purple, C. Ortho-toulidine arsenite, D. Starch iodide
D: Starch iodide
Answer: D: Starch iodide 
Explanation: Indicator in Horrock’s apparatus: Starch iodide.
Indicator in Presumptive coliform test (MPN Multiple Tube Method): Bromocresol purple.