A 4-year-old Caucasian boy is brought to his pediatrician with complaints of abnormal bruising and repeated bacterial infections. A blood workup reveals thrombocytopenia and neutropenia and the presence of numerous small, dense lymphoblasts with scant cytoplasm. Immunophenotyping of the abnormal cells determines them to be extremely primitive B cells, which are CD19+, HLA-DR+, and Tdt+. Which of the following best describes the status of immunoglobulin chain synthesis most likely in these cells?( )

A. IgM monomers inserted in the membrane
B. IgM monomers present in the cytoplasm
C. Mu (m) chains inserted in the membrane
D. Mu (m) chains present in the cytoplasm
E. No immunoglobulin chain synthesis present