This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrical Ultrasonography in the First Trimester, Subject name: Radiology
[{'content': 'Gas shadow in heart and great vessels appears in- \nSelect and explain. \nA. IUD, B. Abortion, C. Still birth, D. None', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., IUD o In intrauterine death (IUD), there is gas in great vessels and chambers of heart - Robert's Sign.", 'role': 'assistant'}]