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': 'Increased level of which of the following indicates contamination of water \nSelect and explain. \nA. Nitrates, B. Nitrites, C. Ammonia, D. Chloride', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ammonia in water is an indicator of bacterial, sewage and animal pollution. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 779", 'role': 'assistant'}]