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: Surgery
Perirectal abscess drainage belongs to 
Select and explain. 
A. Clean surgery, B. Contaminated surgery, C. Clean contaminated surgery, D. Dirty surgery
B: Contaminated surgery
Answer: B: Contaminated surgery 
Explanation: Contaminated surgery :

Wound is exposed to any organism in uncontrolled environment.
Perisectal abscess drainage belongs to this category.