Final answer:
Sebaceous glands produce sebum that lubricates and waterproofs the skin and hair, has antibacterial properties, and prevents water loss, corresponding to that they protect the surface of the skin. The correct option is A.
Step-by-step explanation:
The function that sebaceous glands perform is to lubricate and waterproof the skin and hair. These glands are responsible for generating and excreting sebum, a mixture of lipids, which helps in maintaining the skin's moisture balance, keeping it pliable as well as offering antibacterial properties.
Sebum prevents water loss from the skin in environments with low humidity and is stimulated by hormones, notably becoming more active during puberty. The correct answer to the student's question is A. protect the surface of the skin.
Therefore, the correct option is A.