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 is a gram negative anaerobic bacteria: September 2007 
Select and explain. 
A. Streptococci, B. Bacteroides, C. Actinomyces, D. Clostridium welchii
B: Bacteroides
Answer: B: Bacteroides 
Explanation: Ans. B: Bacteroides