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': 'Earliest ultrasound sign of pregnancy in a transabdominal ultrasound scan is : \nSelect and explain. \nA. Visible gestational sac, B. Apparent embryonic structures, C. Fundal endometrial thickening, D. Identifiable cardiac movements', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Fundal endometrial thickening', 'role': 'assistant'}]