This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: ULTRASOUND, Subject name: Radiology
[{'content': 'Duplex ultrasound is a combination of \nSelect and explain. \nA. A mode and pulse wave doppler, B. B mode and pulse wave doppler, C. M mode and spectral doppler, D. 3D USG and Elastography', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Duplex Scan Combination of B-mode imaging with Pulsed Doppler USG - gives both anatomical & physiological information of vascular system. Colour Duplex Scan Addition of colour frequency mapping - Colour Duplex imaging.', 'role': 'assistant'}]