This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ULTRASOUND, Subject name: Radiology
[{'content': 'Gas shadow in hea and great vessels appears in- \nSelect and explain. \nA. IUD, B. Aboion, C. Still bih, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: IUD ROBE SIGN: Hyperechoic area inside hea and umbilical vein because presence of AIR SPALDING SIGN: Overlapping sutural bones on USG SPALDING SIGN ROBE SIGN', 'role': 'assistant'}]