Transitions, Which Are Changes from _______, Occur _______ Transversions

Transitions, which are changes from _______, occur _______ transversions.

A) purines to purines or pyrimidines to pyrimidines; more often than
B) purines to purines or pyrimidines to pyrimidines; about as frequently as
C) purines to purines or pyrimidines to pyrimidines; less often than
D) purines to pyrimidines or pyrimidines to purines; more often than
E) purines to pyrimidines or pyrimidines to purines; less often than