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': 'All of the following statements about purification of water are true except - \nSelect and explain. \nA. Presence of Clostridial spores indicate recent contamination of water, B. Coliforms must not be detectable in a ny 100 ml sample of drinking water, C. Sodium thiosulphate is used to neutralize chlorine, D. Coliforms may be detected by multiple tube method & indole production', 'role': 'user'}, {'content': "Answer: A \nExplanation: Spores of Clostridium are capable of surviving in water for a longer time than the coliform group of organisms. The presence of Clostridium spores in the absence of coliform group suggest faecal contamination occurred at some remote time. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 781", 'role': 'assistant'}]