Question

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

Explanation:

In a DNA molecule, the complementary strands are held together by hydrogen bonds between nitrogen - containing bases. Adenine pairs with thymine (with 2 hydrogen bonds) and cytosine pairs with guanine (with 3 hydrogen bonds). Sugars and phosphates form the backbone of the DNA strand (linked by phosphodiester bonds), not involved in hydrogen - bonding between complementary strands.

Answer:

B. nitrogen - containing bases