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: Microbiology
Which of the following is anaerobic: 
Select and explain. 
A. E.coli, B. Bacteroides, C. Pseudomonas, D. Klebsiella
B: Bacteroides
Answer: B: Bacteroides 
Explanation: None