Which of the Following Accounts for Allelic Exclusion in Rearrangement

Which of the following accounts for allelic exclusion in rearrangement within the IgH locus?

A) Rearrangement only occurs on one homolog at a time, and once one homolog has successfully rearranged, the other is methylated to produce heterochromatin.
B) Rearrangement is regulated by VpreB and ? 5, which are themselves only expressed at specific times during IgH rearrangement
C) Both homologs rearrange simultaneously, undergoing multiple V-J rearrangements until a productive one occurs.
D) All of the answers promote allelic exclusion in IgH.
E) None of the answers are correct; allelic exclusion does not occur in IgH.