Final answer:
The DNA double helix does not have single-stranded regions.
Step-by-step explanation:
The correct answer is d) Single-stranded regions.
DNA double helix does not have single-stranded regions. The DNA double helix is made up of two strands that are twisted around each other in a helical structure.
These two strands are anti-parallel, meaning that the 3' end of one strand faces the 5' end of the other strand.
The sugar-phosphate backbones form the outer structure of the helix, while the nitrogenous bases (adenine, thymine, cytosine, and guanine) pair up in complementary base pairing manner.