This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamentals in Radiology, Subject name: Radiology
USG is done to visualize all except - 
Select and explain. 
A. Fluid, B. Bile, C. Blood flow, D. Bone
D: Bone
Answer: D: Bone 
Explanation: Bone has high acoustic impendence , hence USG is not used for bone pathologies