The two strands of a DNA molecule are held together by hydrogen bonds between the:

• A. phosphate groups
• B. nitrogenous bases
• C. ribose sugars
• D. deoxyribose sugars

Answer: (B)

Verified step by step guidance

1. Recall the structure of DNA, which consists of two strands forming a double helix.
2. Understand that each strand is made up of a sugar-phosphate backbone and nitrogenous bases attached to the sugars.
3. Recognize that the sugar-phosphate backbone (phosphate groups and deoxyribose sugars) forms the structural framework of each strand, but does not directly hold the two strands together.
4. Identify that the two strands are held together by hydrogen bonds specifically between complementary nitrogenous bases (adenine pairs with thymine, and cytosine pairs with guanine).
5. Conclude that the hydrogen bonding between nitrogenous bases is responsible for holding the two DNA strands together.