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
A 36 years male presented with complain of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is ? 
Select and explain. 
A. Actinomyces israelii, B. Nocardia asteroides, C. Blastomyces dermaiiiidis, D. Crfptosperidium parvum
B: Nocardia asteroides
Answer: B: Nocardia asteroides 
Explanation: Ans. is 'b' i.e., Nocardia asteroides