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
Clostridia is? 
Select and explain. 
A. Gram positive aerobe, B. Gram positive obligate anaerobe, C. Gram negative rods, D. Gram negative bacillus
B: Gram positive obligate anaerobe
Answer: B: Gram positive obligate anaerobe 
Explanation: Gram positive obligate anaerobe REF: Jawetz's microbiology 24th edition chapter 12 "The clostridia are large anaerobic, gram-positive, motile rods"