A nurse is reinforcing teaching with a client who has diabetes mellitus type 1 about sick-day management. Which of the following is the priority action for the nurse to recommend to the client?

A. Monitoring blood glucose every 4 hours is important but secondary to maintaining insulin therapy. B. Maintaining hydration is essential, but it does not address the primary risk of hyperglycemia or diabetic ketoacidosis. C. Reducing carbohydrate intake can worsen blood glucose control; clients should maintain usual intake as tolerated. D. Taking the usual dosage of insulin is the priority because omitting insulin can lead to hyperglycemia and diabetic ketoacidosis, which are life-threatening complications during illness.