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: Social & Preventive Medicine
As per RNTCP guidelines, Multi drug resistance (MDR) TB is defined as resistance to: 
Select and explain. 
A. Rifampicin, B. Rifampicin and isoniazide, C. Rifampicin, isoniazide and ethambutol, D. None of the above
B: Rifampicin and isoniazide
Answer: B: Rifampicin and isoniazide 
Explanation: Confirmed MDR-TB case: MDR-TB suspect is one who is sputum culture positive and whose TB is due to Mycobacterium tuberculosis that are resistant in-vitro to at least isoniazid and rifampicin (the culture and DST result being from an RNTCP accredited laboratory). Ref: Park 21st edition, page 178.