B. Myelodysplastic syndrome (MDS) is the most likely diagnosis. MDS is characterized by dysplastic cells of all three lineages in the bone marrow, leading to peripheral cytopenias. The findings of macrocytic anemia, thrombocytopenia, and Pelger-Huet neutrophils on blood film are consistent with MDS. The bone marrow biopsy also showed a normocellular marrow. MDS commonly presents in the elderly and has no known cause in many cases.