The Secondary Structure of Proteins Is Held Together by Hydrogen

The secondary structure of proteins is held together by hydrogen bonds between which protein sub-structures?

A) The C=O and N-H on amino acid side chains
B) The C=O on the protein backbone and the N-H on the amino acid side chains
C) The C=O on the amino acid side chains and the N-H on the protein backbone
D) The C=O and the N-H on the protein backbone
E) There are no hydrogen bonds involved with secondary structure.