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': 'The investigation of choice for an ectopic pregnancy is – \nSelect and explain. \nA. CT scan, B. Transvaginal USG, C. Serum HCG levels, D. MRI', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Transvaginal ultrasound is the investigation of choice for unruptured ectopic pregnancy.', 'role': 'assistant'}]