Classical MHC Molecules Function as Peptide-Binding Receptors That Present These $\alpha$

Multiple Choice

Classical MHC molecules function as peptide-binding receptors that present these peptides to $\alpha$ : $\beta$ T cells for recognition by $\alpha$ : $\beta$ T-cell receptors. MHC molecules can be detected as far back in evolution as sharks, the same time at which T-cell receptors can be identified. Examination of shark MHC proteins indicates that these molecules likely function identically to human MHC molecules. This conclusion is based on:

A) The conservation of amino acid residues important in peptide binding in both shark and human MHC proteins
B) The observation that MHC genes are highly polymorphic in sharks as well as humans
C) The fact that sharks have both MHC class I and MHC class II molecules
D) The finding that sharks have both classical and nonclassical MHC molecules, like humans
E) The ability to trace the evolution of MHC protein sequences from the earliest vertebrates to humans