Answer: C. Tertiary structure.
Explanation: The overall three-dimensional folded structure of a polypeptide is referred to as the tertiary structure. The structure is due to the relationship between the R-groups of the amino acids that constitute the building blocks of proteins.
The sequence initiated by amino acids that proteins tread is what gives the three dimensional shape to the tertiary state of a polypeptide.
The bond is a major contributing factor for the three dimensional shape of the tertiary structure. This formidable bond is known as the disulfide bond, which is a special kind of chemical covalent bonding.