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
[{'content': 'Distal Acoustic shadow is seen in? \nSelect and explain. \nA. Air, B. Calculi, C. Bone, D. All of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: All of the above REF: Ultrasound Teaching Manual by Matthias Hofer page - 15 In simple terms when sound waves strike an interface which reflects it back, it shows on USG as a hypoechoic or anechoic shadow beyond the structure. It is seen with gas and at interface like bone, calculi and stones.', 'role': 'assistant'}]