Answer:
The correct option is b. myelinated axons from many neurons
Explanation:
White matter is an area which is present in the brain and the spinal cord, that are mainly consists of bundles of myelinated axons, also called tracts. The myelinated axons are the nerve fibres that are surrounded by a lipid-rich substance called myelin.
The presence of the myelin gives the tissue the white colored appearance in contrast to the cerebral cortex which is the grey matter.
Therefore, the myelinated axons from many neurons aggregate together to form the white matter present in the brain and the spinal cord.
