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
All the following statements about purification of water are true except 
Select and explain. 
A. Coliforms must not be detectable in any 100 ml sample of drinking water, B. Presence of clostridial spores indicate recent contamination, C. Sodium thiosulphate is used to neutralize chlorine, D. Coliforms may be detected by multiple tube method and indole production at 44 degrees
B: Presence of clostridial spores indicate recent contamination
Answer: B: Presence of clostridial spores indicate recent contamination 
Explanation: None