In the Diagram Below, the Plane Drawn Behind the Peptide $\alpha$

Multiple Choice

In the diagram below, the plane drawn behind the peptide bond indicates the:

A) absence of rotation around the C-N bond because of its partial double-bond character.
B) plane of rotation around the C _$\alpha$ -N bond.
C) region of steric hindrance determined by the large C=O group.
D) region of the peptide bond that contributes to a Ramachandran plot.
E) theoretical space between -180 and +180 degrees that can be occupied by the $\phi$ and $\Psi$ angles in the peptide bond.