Final answer:
Sebaceous glands primarily supply hair shafts and skin with oily secretions. These glands produce sebum that lubricates and protects the hair and skin while also preventing water loss and inhibiting bacterial growth.
Step-by-step explanation:
The correct answer is C. Sebaceous gland. Sebaceous glands primarily supply hair shafts and skin with oily secretions. These glands produce a lipid mixture called sebum, which is secreted onto the hair and skin to lubricate and protect them. Sebum also has antibacterial properties and helps prevent water loss from the skin.