What Is Meant by the Denaturation of a Protein

What is meant by the denaturation of a protein?

A) Amino acids are removed from the original polypeptide chain, leading to denaturation.
B) Additional carboxyl groups bind to the ends of the polypeptide chain, leading to denaturation.
C) Hydrogen bonds between regions of the polypeptide chain are broken, leading to denaturation.
D) Larger amino acids such as phenylalanine are replaced with smaller amino acids such as cysteine, leading to denaturation.