The correct answer is D  

The goals of therapy for type 2 diabetes include an ideal hemoglobin A1C  level less than 6.5% to 7%. A change in the therapeutic regimen is therefore indicated. The United Kingdom Prospective Diabetes Study demonstrated the progressive nature of type 2 diabetes and secondary failure of both medical nutrition therapy and monotherapy with sulfonylureas. Furthermore, sulfonylurea therapy is frequently associated with weight gain, which worsens insulin resistance. Finally, the maximal effective dosing of sulfonylureas is less than the maximally approved dose. Glycemic control rarely improves with sulfonylurea dosing beyond approximately 50% of the approved maximum amount. Multiple studies have demonstrated the advantage of adding synergistic therapies rather than substituting therapies. The addition of metformin to sulfonylurea is considerably more advantageous than replacing the sulfonylurea in the case of secondary sulfonylurea failure. The pathophysiology of type 2 diabetes suggests a benefit to the combination of an insulin secretagogue, such as glyburide, with an insulin sensitizer, such as metformin. Although the addition of pioglitazone, another insulin sensitizer, has been shown to be effective in decreasing the hemoglobin A1C level, it is associated with further weight gain. Addition of metformin to therapy with an insulin secretagogue appears to be more weight neutral and would thus have relative advantage in a patient with progressive weight gain.