Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form?
A. Ionic bonds join two double-ringed structures in each pair.
B. Hydrogen bonds join two single-ringed structures in each pair.
C. Hydrogen bonds join a double-ringed structure to a single-ringed structure in each pair.
D. Covalent bonds join a double-ringed structure to a single-ringed structure in each pair.
