Which of the Following Structures Does NOT Participate in H-Bond

Multiple Choice

Which of the following structures does NOT participate in H-bond formation?

A) the amino group of cytosine,adenine,and guanine
B) the ring nitrogens at position 3 of pyrimidines and 1 of purines
C) the carbon double bonds found in the bases
D) the carbonyl group at position 4 of uracil and thymine,position 2 of cytosine,and position 6 of guanine