D, because both A and C are correct.
Answer:
Well there are many ways for scientific models to be use like if something was small and you couldn't see it u would have to make a model of that
Explanation:
If this didn't help I'm sorry
Im pretty sure its guanine
A double helix is <span>a pair of parallel helices intertwined about a common axis, especially that in the structure of the DNA molecule. or in other words a double spiral.</span>
