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': 'Earliest sign of fetal life is best detected by \nSelect and explain. \nA. X-Ray, B. Feto scopy, C. Real time USG, D. Doppler', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. Doppler Doppler is an interpretation of audible signals of USG By listening fetal hea sounds and seeing blood flow, we can detect fetal life at earliest.', 'role': 'assistant'}]