The rungs are composed of hydrogen bonded paired Nitrogenous Bases. These pairings are Adenine to Thymine and Guanine to Cytosine.
Explanation:
As I think option D is the correct one.
Answer: D. adaptations that organisms make to the environment during their lifetimes.
Adaptation is a process in which changes occurs in an organism so as to make it better suited for the environment. It is the result of natural selection. In adaptation the traits of an organism gets modified by the process of natural selection which results in evolution of an organism.
