Which of the following is one of the four chemicals that compose the rungs of the DNA ladder?

The correct answer identifies the chemical that makes up the rungs of the DNA ladder as a base. In the structure of DNA, which is commonly depicted as a twisted ladder or double helix, the rungs are composed of nucleotide base pairs. These bases are adenine (A), thymine (T), cytosine (C), and guanine (G), which pair specifically (A with T and C with G) to form the rungs of the ladder.

Each base is attached to a sugar and phosphate molecule, forming the backbone of the DNA structure, but it is the bases that actually make up the rungs of the ladder. This is fundamental in understanding how genetic information is stored and transferred in living organisms. The unique sequences of these bases encode the instructions for making proteins and function in various cellular processes.

The other options - protein, lipid, and carbohydrate - are macromolecules that serve different functions in biological systems. Proteins are made up of amino acids and play roles in structure and function of cells. Lipids are primarily involved in energy storage and forming cell membranes. Carbohydrates mainly provide energy and structural support, but none of these are components of the DNA ladder itself.