Answer:
B. Hydrogen bonds
Step-by-step explanation:
Hydrogen bonds are the weak attractive bonds that are formed between a partially positive hydrogen atom and an electronegative atom carrying a partial negative charge.
The nitrogenous bases of two strands of a DNA double helix are held together by hydrogen bonds. Adenine forms two hydrogen bonds with thymine base while guanine forms three hydrogen bonds with cytosine base.
These hydrogen bonds between the complementary nitrogenous bases of a double helix hold the two strands of DNA together.