Which Pairs of Bonds Within a Peptide Backbone Show Free $\alpha$

Which pairs of bonds within a peptide backbone show free rotation around both bonds?

A) C _$\alpha$ -C and N-C _$\alpha$
B) C=O and N-C
C) C=O and N-C _$\alpha$
D) N-C and C _$\alpha$ -C
E) N-C _$\alpha$ and N-C