Deoxyribonucleic acid (DNA) is composed of two chains of nucleotides that form a double helix, which resembles a ladder.
Each nucleotide is formed by a phosphate group, deoxyribose (a sugar), and a nitrogenous base.
The phosphate groups and the deoxyribose alternate with each other and make the rails of the ladder, while the nitrogenous bases of one chain are paired to the ones of the other, and make the rungs of the ladder.
This means the right answer is C. nitrogenous base
