A 20 - year - old woman has had worsening fatigue for the past year . On examination her mucus membranes are pale . No hepatosplenomegaly is present . Her CBC shows a Hgb of 7.1 g / dl . , Het 19.9 % , MCV 67 fl , platelet count 190,000 / uL . , and WBC count 5,400 / uL . There is no history of drug ingestion . Which of the following is the most likely etiology for her findings ?
A. Cobalamin deficiency
B. G6PD deficiency
C. Folate deficiency
D. Iron deficiency