Answer:
The correct answer will be option-D.
Step-by-step explanation:
The nervous system is a system composed of nervous tissue which comprised of the neurons and the associated cells called glial cells.
The neurons are the main transmitting cells of the nervous system which are surrounded, protected and nourished by the glial cells or neuroglia. These glial cells include Schwann cells, astrocytes, oligodendrocytes, satellite cells, microglia and ependymal cells.
In the given question, the answer will be all of the above as the Schwann cells help in the formation of the myelin sheath in the PNS while astrocytes help in the metabolic process.
Thus, option-D is the correct answer.