Which of the following is correct?
a. the purine g bonds with the purine
c. b. the purine c bonds with the pyrimidine g.
c. the pyrimidine c bonds with the purine g.
d. the pyrimidine c bonds with the pyrimidine g.

The correct answer is C. Cytosine or C is a pyrimidine while Guanine or G is a purine. Purines are double ringed nitrogenous bases namely adenine and guanine while pyrimidines are single ringed nitrogenous bases namely cytosine, thymine and uracil. According to base pairing rules, adenine will always pair with thymine while guanine will always pair with cytosine in DNA. In RNA, Guanine will always pair with cytosine while adenine will always pair with uracil instead of thymine. RNA does not have thymine in its structure.