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: Radiology
40 year old male farmer who has livestock was admitted with paroxysms of cough and expectoration. Clinical examination was normal. Chest X-ray showed a large thin walled cavity containing membranes in the lower lobe of the left lung with left pleural effusion. CT scan of the chest revealed a 'water lily' sign. What is the most probable diagnosis? 
Select and explain. 
A. Echinococcus infection, B. Aspergillosis, C. Interstitial lung disease with TB, D. Amebic lung abscess
A: Echinococcus infection
Answer: A: Echinococcus infection 
Explanation: Water lily sign although rarely seen is pathognomonic of echinococcosis. Cyst with a freely floating endocyst.