Which One of the Following Is NOT True of the Constant

Which one of the following is NOT True of the constant (C) regions of antibodies?

A) The constant regions are the same or nearly the same on all antibodies of a given class.
B) The constant regions form the "stem" of an antibody.
C) The constant regions determine the specific type of antibody class formed.
D) The constant regions form an antigen-binding site.
E) The constant regions determine how an antibody class will carry out its immune role.