This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins bonds and structure, Subject name: Biochemistry
Alpha helix is stabilized by? 
Select and explain. 
A. Disulfide linkage, B. Covalent bonding, C. Hydrophobic interactions, D. Hydrogen bonds
D: Hydrogen bonds
Answer: D: Hydrogen bonds 
Explanation: Secondary Structure includes * Alpha helix * Beta pleated sheet * Beta bend or turn * Alpha chain in collagen (not alpha helix) Structure Bonds Primary structure Covalent/amide/peptide bond Secondary structure Hydrogen bonds Teiary structure Disulphide, Hydrogen, Hydrophobic and Ionic bond Quaternary structure Hydrogen, hydrophobic and ionic bond