A would be my best answer
If the nitrogenous base is made of two rings that means it's a purine(adenine, guanine), if it's made of one ring that means it's a pyrimidine(cytosine,thymine, uracil).
Arising of a new species is not a rare thing. Organisms are always in a competition to survive long. Speciation, as what they call it, is happening from time to time because organisms evolve in order to adapt to the environment where they are in. However, this process is a slow one thus it is almost impossible to see a new species arising.
