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': 'All of the following are pain insensitive structures except \nSelect and explain. \nA. Choroid plexus, B. Ventricular ependyma, C. Brain parenchyma, D. Falx cerebri', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Relatively few cranial structures are pain-producing; these include the scalp, meningeal aeries, dural sinuses, falx cerebri, and proximal segments of the large pial aeries. The ventricular ependyma, choroid plexus, pial veins, and much of the brain parenchyma are not pain-producing. Ref Harrison 20th edition page 85', 'role': 'assistant'}]