Question

1 the purines are _, and the pyrimidines are _ a cytosine and thymine; adenine and guanine b adenine and thymine; guanine and cytosine c adenine and cytosine; guanine and thymine d adenine and guanine; cytosine and thymine

Explanation:

Purines are double - ringed nitrogenous bases. Adenine (A) and guanine (G) are purines. Pyrimidines are single - ringed nitrogenous bases. Cytosine (C) and thymine (T) are pyrimidines.

Answer:

D. adenine and guanine; cytosine and thymine