B Cell Development in the Bone Marrow Is an Inherently

B cell development in the bone marrow is an inherently wasteful process. Nearly half of the pro-B cells produced will die without progressing on to the next stage of B cell development. This massive loss of pro-B cells is due to:

A) The failure of many pro-B cells to up-regulate Pax5 and become committed to the B cell lineage.
B) The inability of many pro-B cells to proceed with rearranging a V_H to their rearranged DJ_H sequence.
C) Large insertions of untemplated nucleotides into the rearranged gene by TdT.
D) Detrimental DJ_H rearrangements on both alleles of the immunoglobulin heavy chain locus.
E) The failure of the pro-B cell to make a complete immunoglobulin heavy chain protein.