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': 'Most valuable diagnostic test in a case of suspected ectopic pregnancy: \nSelect and explain. \nA. Serial (3-hCG levels, B. Transvaginal USG, C. Progesterone measurement, D. Culdocentesis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Transvaginal ultrasound Repeat from Nov 09 Q no.161', 'role': 'assistant'}]