Work Step by Step
The backbone of the DNA molecule is made up of alternating sugar and phosphate groups. The rungs of the helix of DNA is made up of the nitrogenous base pairs of adenine-thymine and cytosine-guanine. Looking at the choices, we can determine that options A, C, and D are all incorrect. Only B is correct because it states that sugar and phosphates make up the backbone of the DNA helix.