This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
[{'content': 'Which of the following is the most commonly used MR sequence for non-contrast angiography? \nSelect and explain. \nA. Time-of-flight (TOF), B. Phase contrast, C. TRUFI, D. Aerial spin labeling', 'role': 'user'}, {'content': 'Answer: A \nExplanation: .', 'role': 'assistant'}]