Answer to Question 1
ANS: D
By definition, the red count, hemoglobin, and hematocrit are all decreased in anemia, so those cannot be used to separate one cause from another. However, the RDW describes whether the red cell population is homogenous or heterogeneous with respect to size. Combining it with the MCV can provide very useful information as to possible causes for an anemia.
Answer to Question 2
ANS: C
Folate deficiency is a macrocytic anemia. Iron deficiency anemia (stage 3) and thalassemia are microcytic; aplastic anemia is normocytic.