A client with a leukemia has been placed on methotrexate. Which of the following mechanism of actions below describes this medication?

A. Stops fungal growth: Methotrexate is not an antifungal medication. This mechanism of action applies to drugs like azoles or polyenes, which are used to treat fungal infections. B. Alters pH level: Altering pH is a mechanism used by some antacids or alkalinizing agents, not methotrexate. C. Inhibits replication by blocking folic acid synthesis: Methotrexate is an antimetabolite that inhibits dihydrofolate reductase, an enzyme involved in folic acid synthesis. This inhibition impairs DNA synthesis, which is crucial in treating leukemia and other cancers. D. Inhibits helper T cells: This mechanism of action is more closely related to immunosuppressive agents like cyclosporine or tacrolimus, which are used for preventing transplant rejection.