The second option is the best answer.
Proteins are complex polymers of amino acids. They are folded into 3 dimensional structures . This folding defines not only the size and shape of the protein, but also its function.
The folding of a protein allows for interactions between amino acids that may be distant from each other in the primary sequence of the protein. In enzymes, some of these amino acids form a site in the structure that catalyzes the enzymatic reaction. This site is called the active site.
The correct answer is "It is a complex, folded chain that helps regulate cell processes".
The monomers of a protein are amino acids. Many amino acids form a long linear chain to become peptides which is the primary structure of a protein molecule. These primary structures further arrange themselves in a local space to form secondary structures like alpha helix or beta sheet. Once a secondary structure of protein is formed, it folds itself by making interactions with other amino acids which are situated at a far off location to form a tertiary structure. The tertiary structures are therefore known to form global spacial arrangement rather than forming local spatial arrangement. Even after the formation of a tertiary structure, in some proteins many tertiary structures combine to form complex quaternary structures. It is only tertiary and quaternary structures of proteins which are usually considered as functional. Proteins serve the function of regulation of cellular processes in the form of enzymes like DNA polymerases, RNA polymerases, hormones etc.