The correct answer is a) white.
Myelinated nerve fibers appear white due to the presence of myelin, a fatty substance that insulates the nerve fibers and increases the speed of electrical signal transmission. The high lipid content of myelin affects how light interacts with the fibers, making them appear white when viewed in cross-section. In contrast, unmyelinated fibers lack this insulation and typically appear gray, which is why areas of the brain and spinal cord with a high concentration of myelinated fibers are often referred to as ‘white matter’.