What are the four nitrogenous bases that make up DNA?

The four nitrogen bases that are found in deoxyribonucleic acid (DNA) are adenine, cytosine, guanine, and thymine.

Thymine and cytosine comprise of one -carbon nitrogen ring and also called pyrimidines, while two carbon nitrogen ring is present in adenine and guanine and also called purines. Purines has larger in size because of extra carbon nitrogen ring.

b. the carbon cycle ensures living things have a source of hydrogen