Final answer:
Option d) Friction is the scalp manipulation that stimulates the sebaceous glands to produce sebum, a natural oil that moisturizes and protects the hair and scalp.
Step-by-step explanation:
Of the primary scalp manipulations, the manipulation that stimulates the sebaceous glands which produce the natural oil (sebum) is d) friction.
Friction involves using the fingers and palms to create pressure against the scalp, which in turn stimulates the sebaceous glands to produce sebum. This natural oil helps to moisturize and protect the hair and scalp, maintaining the scalp's health and preventing the hair from becoming dry and brittle.