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
The heart to the activated sludge process is – 
Select and explain. 
A. Primary sedimentation tank, B. Sludge digestor, C. Aeration tank, D. Final settling tank
C: Aeration tank
Answer: C: Aeration tank 
Explanation: None