What are appropriate actions for a registered nurse (RN) caring for a 14-month-old diagnosed with severe iron deficiency anemia, admitted for blood transfusion, and started on oral iron supplementation but the RN notices dark black stool?

a) Notify the healthcare provider immediately and monitor vital signs closely.
b) Document the findings and continue to monitor the stool color.
c) Increase the dosage of oral iron supplementation to address the anemia.
d) Discontinue the oral iron supplementation and switch to a different treatment