Final answer:
Sebaceous glands are connected to the hair follicles and produce oil called sebum, which protects the surface of the skin.
Step-by-step explanation:
The correct answer is A) Sebaceous gland. Sebaceous glands are connected to the hair follicles and produce an oily substance called sebum. This sebum acts as a protective barrier on the surface of the skin, waterproofing it, preventing it from drying out, and inhibiting the growth of microorganisms.