A nurse is reinforcing teaching about preventing long-term complications of retinopathy and neuropathy with an older adult client who has diabetes mellitus. Which of the following actions is the most important for the nurse to include in the teaching?

A. "Plan to have an eye examination once per year.": Detects retinopathy early but is secondary prevention, not the key long-term strategy. B. "Examine your feet carefully every day.": Helps detect neuropathic injuries early but does not directly prevent microvascular damage. C. "Wear closed-toed shoes daily.": Provides protection from trauma but does not address systemic complications. D. "Maintain stable blood glucose levels.": Tight glycemic control is the single most important factor in preventing progression of retinopathy and neuropathy.