This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Medicine
The definitive diagnosis of Pneumocystis carinii pneumonia is - 
Select and explain. 
A. Serological test, B. Chest X-ray, C. Finding cysts in tissue specimens, D. ) CT scan of thorax
C: Finding cysts in tissue specimens
Answer: C: Finding cysts in tissue specimens 
Explanation: Its life cycle begins when cysts rupture and release sporozoites, which mature into trophozoites that eventually form cysts. The diagnostic methods for P. carinii pneumonia (PCP) have progressed from open lung biopsy to bronchoalveolar lavage (BAL) and induced sputum analysis . Ref Harrison20th edition pg 1056