The sequence of the atoms in the polypeptide backbone varies between different proteins nonpolar amino acids tend to be found in the interior of proteins. there is free rotation around all covalent bonds in the polypeptide backbone peptide bonds are the only covalent bonds that can link together two amino acids in proteins.

Nonpolar amino acids tend to be found in the interior of proteins

Explanation:

As you may already know, proteins are macromolecules formed by a succession of smaller molecules known as amino acids. Most living things, including humans, use only about twenty different types of amino acids to build their proteins. These amino acids can be polar and nonpolar, and their location in this protein can alter their function in the body.

A general feature of proteins is the localization of nonpolar amino acids within the protein while the polar or charged amino acids lie on the surface of the protein. Hydrophobicity is a very important factor in protein stability and a significant role is attributed to the nonpolar effect on protein folding.

Sulfur-containing amino acids may also have nonpolar characteristics, especially in the case of cysteine involved in the formation of sulfur bridges. The phenylalanine side chain is strongly nonpolar. Similarly tryptophan and tyrosine are partially hydrophobic in spite of the presence of the nitrogen atom or the -OH group.

it's c. (to reduce the greenhouse effect/carbon gasses)