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': 'Acoustic shadow on USG is due to: \nSelect and explain. \nA. Reflection, B. Refraction, C. Aefact, D. Absorption of waves', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Reflection', 'role': 'assistant'}]