Question

in a dna molecule, the complementary strands are joined at the nucleotides by hydrogen bonds between what? a nitrogen - containing bases b phosphates c sugars

Explanation:

In a DNA molecule, the complementary strands are held together by hydrogen - bonds between the nitrogen - containing bases (adenine pairs with thymine, and cytosine pairs with guanine). Phosphates and sugars form the backbone of the DNA strand and are not involved in the hydrogen - bonding between complementary strands.

Answer:

A. nitrogen - containing bases