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