Choice A rationale:
Triple-drug therapy is not the standard treatment for pernicious anemia after a gastrectomy. Pernicious anemia is primarily caused by vitamin B12 deficiency due to the absence of intrinsic factor, which is essential for vitamin B12 absorption.
Choice B rationale:
IV therapy is a broad term and does not specify the treatment for pernicious anemia. In the context of pernicious anemia, cobalamin replacement therapy administered via intramuscular injections is the preferred treatment.   
Choice C rationale:
Quadruple-drug therapy is not a recognized treatment for pernicious anemia. The primary treatment for pernicious anemia involves cobalamin replacement therapy to address the vitamin B12 deficiency.
Choice D rationale:
Cobalamin replacement therapy is the appropriate treatment for pernicious anemia after a gastrectomy. Since the patient lacks intrinsic factor, which is necessary for vitamin B12 absorption, cobalamin replacement therapy bypasses the need for intrinsic factor and provides the necessary vitamin B12 directly.