The correct answer is "tertiary." Translation is a process performed by ribosomes to link amino acids together in a chain, and the order of the amino acids is based on a code from mRNA. The order of the amino acids in the chain is the primary structure. The secondary structure is the folding in that chain, mainly based on hydrogen bonds between parts of the chain and the surrounding water molecules. The tertiary structure is the actual three-dimensional structure of the protein. Disulfide bonds are covalent bonds between cysteine residues and are stronger than hydrogen bonds and give a stable, three-dimensional structure to what was originally just a chain of amino acids.

The primary structure of a protein is simply the linear amino acid sequence from which the protein is made. "Secondary structure" refers to the folding and coiling of this single strand as it interacts with itself, forming hydrogen bonds between amino acids of that strand. Alpha helices and beta-pleated sheets are two different types of secondary structures that can be formed by hydrogen-bonding between amino acids of a protein sequence that has folded over onto itself. "Tertiary structure" refers to the final three-dimensional structure of a single protein subunit. "Quaternary structure" refers to the non-covalent interactions between multiple protein subunits which come together to form a larger protein.