This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'A patient with suspected subarachnoid haemorrhage presents with blood isolated in the fouh ventricle on a CT scan. Aneurysmal rupture is likely to have resulted from \nSelect and explain. \nA. Posterior Inferior Cerebellar Aery Aneurysm, B. Anterior Communicating Aery Aneurysm, C. Posterior Communicating Aery Aneurysm, D. Basilar Aery Tip Aneurysm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: *Saccular aneurysm at size of >7mm and at top of basilar aery and at origin of posterior communicating aery are at greater risk of rupture . Ref Harrison20th edition pg 2445', 'role': 'assistant'}]