Final answer:
A) Proteins
The characteristics described, including acting as enzymes and containing specific elements such as C, H, O, N, and sometimes S, relate to proteins, which are complex macromolecules with a wide range of functions in living organisms.
Step-by-step explanation:
The characteristics mentioned in the question, such as functioning as enzymes, containing carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S), and being structural materials, are descriptive of proteins. Proteins are integral components within biological systems and perform a wide range of functions, including serving as enzymes which facilitate biochemical reactions, providing structural support, and acting in various cellular processes. The building blocks of proteins, amino acids, link together to form long chains known as polypeptides, which then fold into complex structures to carry out specific biological functions.