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
[{'content': 'Which of the following is not true about water quality estimation – \nSelect and explain. \nA. Clostridium spores indicate recent contamination, B. Not more than 5% samples should have coliforms, C. Sodium thiosulfate added to neutralize chlorine, D. Coliforms must not be detectable in 100ml sample', 'role': 'user'}, {'content': "Answer: A \nExplanation: Option 'a'\n\nColiform organism → Most commonly used bacteriological indicates\nFaecal streptococci → Recent faecal pollution of water.\nSpores of Cl. perfringence (in the absence of coliform group) → Remote faecal contamination of water.\n\nAbout other options\nOption 'b. & d'\n\nTotal coliform bacteria must not be detectable in any 100 ml of sample.\nBut, In case of large supplies, where sufficient samples are examined, coliform bacteria must not be present in 95% of samples taken throughout any 12 months period → Not more than 5% samples should have Coliforms.\n\nOption 'c'\n\nSodium thiosulfate is used to dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers.\nIt is also used to lower chlorine levels in swimming pools and spas following superchlorination.", 'role': 'assistant'}]