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
Which of the following is the commonest cause of farmer's lung? 
Select and explain. 
A. Micropolyspora faeni, B. Thermoactinomyces sacchari, C. Mycobacterium bovis, D. None of the above
A: Micropolyspora faeni
Answer: A: Micropolyspora faeni 
Explanation: Farmer's lung is caused due to inhalation of mouldy hay or grain. Thermophillic actinomyeces, commonly Micropolyspora faeni is the common cause of farmer's lung. Ref: Park 21st edition, page 748. Chapter: Occupational health.