Answer:
A. They are the four nitrogenous bases found in DNA.
Step-by-step explanation:
Nitrogenous bases are compounds that are part of the composition of DNA and RNA, which are the nucleic acids found in living organ cells.
They are five and can be classified into two types:
Purine or purine bases - adenine and guanine
Pyrimidine or pyrimidine bases - cytosine, thymine and uracil.