The Difference Between an Antibody Allotype and Isotype Is

The difference between an antibody allotype and isotype is:

A) isotype is the difference in constant regions; allotype are differences within isotypes
B) allotype is the difference in constant regions; isotype are differences within allotypes
C) isotype is the difference in constant regions; allotype are alternations in the hypervariable regions
D) isotype are alternations in the hypervariable regions; allotypes are differences within isotypes
E) isotype are alternations in the hypervariable regions of one person; allotypes are alternations in the hypervariable regions among a species