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
Increased level of which of the following indicates contamination of water 
Select and explain. 
A. Nitrates, B. Nitrites, C. Ammonia, D. Chloride
C: Ammonia
Answer: C: Ammonia 
Explanation: 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