15. Which of the following is NOT an example of a checkpoint in lymphocyte development that contributes to the selective maturation of cells with useful antigen receptors? (A) B cell precursors that cannot express TLR die by apoptosis. (B) Developing T cells that fail to express TCR α chains die by apoptosis. (C) Developing T cells that recognize self-major histocompatibility complex (MHC) molecules with high affinity die by apoptosis. (D) Immature B cells that bind to self-antigen with high affinity die by apoptosis. (E) T cell precursors that cannot express TCR β chains die by apoptosis.