This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Water, Subject name: Social & Preventive Medicine
Indicator of Remote contamination of water 
Select and explain. 
A. Fecal Streptococci, B. Clostridium Perfirengens, C. E. Coli, D. Salmonella Typhi
B: Clostridium Perfirengens
Answer: B: Clostridium Perfirengens 
Explanation: Bacteriological Indicators of Water Quality E Coli: Best indicator. Ideally water should be coliform free except large urban water supplies where up to 5% contamination is acceptable if samples are taken up to 1year. For this screening test used is presumptive coliform count, MPN (Most Probable Number) and multiple tube test. Diagnostic test is EIJKMAN'S test. Faecal streptococci: Best tells recent contamination Clostridium perfringens: Best tells remote contamination