Final answer:
Cholesterol is a key steroid with a four-ring hydrocarbon structure, essential for cell membranes and the production of other steroid hormones in the body.
Step-by-step explanation:
A classic example of a steroid that fits the category is cholesterol. Cholesterol is an essential lipid molecule with a steroid skeleton at its core. Structurally, it consists of four fused hydrocarbon rings, which serve as the foundation for all sterols produced in the human body. These rings are typically denoted as A, B, C, and D. Cholesterol is vital for maintaining cell membrane fluidity and is also the precursor from which the body synthesizes other steroid hormones, such as sex hormones and corticosteroids.