This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Imaging of Alveolar Lung Disease, Subject name: Radiology
Floating water lily sign is seen in 
Select and explain. 
A. Aspergillosis, B. Hamartoma, C. Hydatid cyst, D. Cavitating metastasis
C: Hydatid cyst
Answer: C: Hydatid cyst 
Explanation: Ans. is 'c' i.e. Hydatid cyst Separated membranes floating with the cyst give the appearance of water lily.It is pathognomonic of hydatid cyst.