Which gland is responsible for secreting oil to the skin surface?

The sebaceous gland is the correct choice because it is specifically designed to produce and secrete an oily substance known as sebum. This oil plays a crucial role in maintaining the health of the skin and hair. Sebum helps to lubricate the skin, providing a barrier that prevents dryness and cracking, while also offering some antibacterial properties that protect the skin from microbial infections.

In contrast, sweat glands, which include both apocrine and eccrine glands, are primarily responsible for thermoregulation through the process of sweating, helping to cool the body. These glands secrete a watery fluid that helps with temperature regulation but do not produce the oily secretion characteristic of sebaceous glands.