Final answer:
A B12 deficiency anemia is most likely to be macrocytic, characterized by larger-than-normal red blood cells.
Step-by-step explanation:
A B12 deficiency anemia is most likely to be macrocytic. Macrocytic anemia is characterized by larger-than-normal red blood cells. In the case of B12 deficiency, the lack of vitamin B12 affects the normal production of DNA in the bone marrow, leading to the production of abnormally large red blood cells. This can be observed through a blood test called mean corpuscle volume (MCV), which measures the size of red blood cells.