Which statements about MHC molecules are correct?
A. Class I MHC molecules are composed of two non-covalently associated glycoproteins, a and ẞ chains.
B. MHC genes are polymorphic.
C. Class I MHC molecules are expressed on most nucleated cells.
D. Class II MHC molecules are restricted to B-cells, macrophage and dendritic cells.
Choose the correct answer from the options given below: