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 64 year old lady Kamla complains of severe unilateral headache on the right side and blindness for 2 years. On examination there is a thick cord like structure on the lateral side of the head. The ESR is 80 mm/hr in the first hour. The most likely diagnosis is - \nSelect and explain. \nA. Temporal arteritis, B. Migraine, C. Cluster headache, D. Sinusitis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]