Aplastic anemia: anemia, leukopenia, thrombocytopenia
CML, i.e. leukemias: anemia, ↓ mature WBC, ↓ plt, peripheral blood smear shows mature & maturing granulocytes (FA 2020, p. 432)
β-thalassemia major: microcytic, hypochromic anemia with target cells and anisopoikilocytosis, skeletal deformities, etc. (FA 2020, p. 418)
Cobalamin deficiency: d/t malabsorption, pancreatic insufficiency, gastrectomy, or insufficient intake, neurological Sx
Personally, I got this wrong, because to me, the RBCs in that smear looked both larger and more irregularly shaped, so in hindsight, I really should've honed in more on the HPI, i.e. the patient really has anemia and no other relevant PMx.