Which one of the following is NOT true of the gene segments that combine to make up a heavy chain gene?

  •  A V segment and a J segment are preselected by an antigen to make up the variable-region portion of the gene.
  •  V, D, and J segments combine to encode the antigen-binding site.
  •  Many V region segments are available.
  •  Several J segments and several D segments are available.