Answer:
The correct answer is constant thickness.
Step-by-step explanation:
A DNA double helix is long and contain nitrogen bases in the interior.The nitrogen base of one strand forms hydrogen boding with its complementary base of the other strand.
But DNA does not contain constant thickness because of its helical structure.If the DNA structure properly studied then one can notice that the thickness of some portion of DNA is more forming the major groove whereas the thickness of some particular region is less that generates the minor groove.