Answer:
b) Phosphodiester bonds.
Step-by-step explanation:
The DNA double helix is held together by hydrogen bonds between complementary base pairs (option a), and the strands run antiparallel to each other (option c). However, the covalent bonds between base pairs are not present in DNA; instead, the covalent bonds are formed between the sugar and phosphate groups, creating the backbone of the DNA molecule. These covalent bonds are known as phosphodiester bonds (option b).