This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'CSF is formed by \nSelect and explain. \nA. Arachnoid villi, B. Venous plexus, C. Choroidal plexus, D. Subformical nucleus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The CSF occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain, as well as the central canal of the spinal cord. CSF serves several purposes: Buoyancy Protection Chemical stability Clearing waste Ref: guyton and hall textbook of medical physiology 12 edition page number: 813,814,815', 'role': 'assistant'}]