The cerebrospinal fluid (CSF) is a clear watery nutritional fluid containing sodium chloride, potassium, glucose, and various proteins.
It fills the space between the arachnoid and pia mater of the central nervous system (CNS), the ventricles of the brain and the central canal of the spinal cord.
It is secreted by the choroid plexuses.
In addition to providing nutritional supply to the brain, the CSF also removes by-products of metabolism and also serves to provide a fluid cushion to protect the brain from injury.
CSF is secreted by the choroid plexuses. Hence, the correct answer is option a.