This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Headache, Subject name: Medicine
[{'content': 'The pain of migraine headache is due to - \nSelect and explain. \nA. An idiopathic neuropathy, B. Reflex vasodilation of constricted vessels, C. Constriction of cranial arteries, D. Psychogenic overlay', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans- B Reflex vasodilation of constricted vessels', 'role': 'assistant'}]