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
The factor which promotes virulence of M. tuberculosis - 
Select and explain. 
A. Wax D, B. Cord factor, C. Muramyl dipeptide, D. Mycolic acid
B: Cord factor
Answer: B: Cord factor 
Explanation: None