The correct statement about peptides and proteins is

1. A. Tertiary structure of proteins has two or more polypeptide subunits
2. B. Only the proteins having a quaternary structure are biologically active
3. C. In -pleated sheet structures, peptide chains are held together by intermolecular hydrogen bonds
4. D. In -helices, the polypeptide chain is twisted into a left-handed screw (helix) through intramolecular hydrogen bonds

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