The helical structure of protein is stabilized by??

The helical structure of protein is stabilized by:
[A]hydrogen bonds
[B]ether bonds
[C]peptide bonds
[D]dipeptide bonds

Solution=

• The helix is common in the secondary structure of proteins and is a right hand-spiral conformation (i.e. helix) 
• In helix structure, every backbone N−H$N-H$ group donates a hydrogen bond to the backbone C=O$C=O$ group of the amino acid located three or four residues earlier along the protein sequence.