Answer:
The correct answer would be pairs of nitrogen bases.
DNA (deoxyribonucleic acid) is a double helical structure formed by two strands of DNA.
Deoxyribose sugar and phosphate are linked with phospho-di-ester bond and serve as the backbone of the DNA strands.
Nitrogenous bases are attached to the sugar with the help of glycosidic bond.
Nitrogenous base of one strand forms hydrogen bonds with the nitrogenous bases of the other strands to provide the stability to the structure.
