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: Medicine
[{'content': 'A 35 year old lady Malti has unilateral headache, nausea, vomiting and visual blurring. The diagnosis is - \nSelect and explain. \nA. Cluster headache, B. Glaucoma, C. Subarachnoid haemorrhage, D. Posterior fossa cyst', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]