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: Dental
The heart of activated sludge process is? 
Select and explain. 
A. Aeration tank, B. Primary sedimentation, C. Digestion tank, D. Secondary sedimentation tank
A: Aeration tank
Answer: A: Aeration tank 
Explanation: Sludge is managed aerobically; Aeration which is the heart of the sludge process is done in aeration tank.