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: Gynaecology & Obstetrics
[{'content': "In a pregnant women of 28 weeks gestation IUD is earliest demonstrated on X-ray by : \nSelect and explain. \nA. Increased flexion, B. Overlapping of cranial bones, C. Spalding's sign, D. Gas in vessels", 'role': 'user'}, {'content': 'Answer: D \nExplanation: Gas in vessels', 'role': 'assistant'}]