Correct Option: C

Although similar to Class I, the MHC Class II molecule is composed of two membrane spanning proteins. Each chain is approximately 30 kDa in size, and made of two globular domains. The domains are named α-1, α-2, β-1 and β-2. The two regions farthest from the membrane are α-1 and β-1. The two chains associate without covalent bonds. The MHC molecules ability to present a wide range of antigenic peptides for T cell recognition requires a compromise between broad specificity and high affinity. Class II molecules are dimers consisting of an α and β polypeptide chain. Each chain contains an immunoglobulin like region, next to the cell membrane. The antigen binding cleft, composed of two α-helices above a β-pleated sheet, specifically specifically binds short peptides, about 15 to 24 residues long. The amino acid sequence around the binding site, which specifies the antigen binding properties, is the most variable site in the MHC molecule.