The nitrogenous bases guanine and adenine are A. purines. B. a phosphate group. C. pyrimidines. D. a sugar group.

The nitrogenous bases guanine and adenine are A. purines.

Explanation:

Adenine and guanine are purines, whereas the other two bases in DNA (thymine and cytosine) are pyrimidines.  The main difference between purines and pyrimidines is the number of rings that the base has: purines have two rings while pyrimidines only have one ring.  

In addition, phosphate group and sugar group cannot be the answer to this question because these two elements in addition to a nitrogenous base makes up a nucleotide.

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