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 patient with suspected subarachnoid haemorrhage presents with blood isolated in the fourth ventricle on a CT scan. Aneurysmal rupture is likely to have resulted from - \nSelect and explain. \nA. Posterior Inferior Cerebellar Artery Aneurysm, B. Anterior Communicating Artery Aneurysm, C. Posterior Communicating Artery Aneurysm, D. Basilar Artery Tip Aneurysm', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]