This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contrast Agents, Subject name: Radiology
[{'content': 'All are features of a normal venous doppler except? \nSelect and explain. \nA. Triphasic pattern, B. Flow Ceases with Valsalva, C. Flow Augmentation with Distal Compression, D. Compressibility', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Normal Venous doppler is Monophasic with Respiratory and Cardiac Phasicity. High Resistance Peripheral Aeries show a Triphasic pattern.', 'role': 'assistant'}]