The molecules of living matter that provide building blocks are mostly based on:

Explanation

Carbon forms four covalent bonds and can make stable chains, rings, and complex structures, allowing it to serve as the backbone of carbohydrates, lipids, proteins, and nucleic acids. Nitrogen and hydrogen are important elements but do not provide the same versatile framework for most biological molecules. Students may choose nitrogen because it is present in proteins and nucleic acids, but carbon is the principal structural basis.