A nurse is providing discharge teaching to a client who has diabetes mellitus and a new prescription for regular and NPH insulin. Which of the following statements by the client indicates an understanding of the teaching?

Insulin therapy management involves the precise coordination of short-acting and intermediate-acting agents to mimic physiological glucose regulation. Regular insulin acts rapidly, whereas NPH insulin contains protamine to delay absorption and extend the duration of action. Proper mixing technique is vital to maintain the integrity of each medication and ensure accurate glycaemic control without causing cross-contamination. Rationale: A. Injecting air into both vials is the correct first step when mixing insulins to prevent the creation of a vacuum. The nurse must teach the client to inject air equal to the dose into the NPH vial first, followed by air into the regular vial. This equalization of pressure allows for the smooth withdrawal of the liquid medication without contaminating the regular insulin with NPH. B. Shaking insulin vials vigorously is contraindicated as it creates air bubbles that interfere with accurate dose measurement and can denature the protein molecules. Instead, NPH insulin, which is a suspension, should be gently rolled between the palms to redistribute the particles. Regular insulin is a clear solution and does not require any agitation or rolling before withdrawal from the vial. C. Drawing up NPH insulin first is an incorrect technique that risks contaminating the clear regular insulin vial with the cloudy protamine from the NPH. The standard protocol is to draw the "clear before cloudy" (regular before NPH) to ensure the fast-acting insulin remains pure. Contamination of the regular vial with NPH would inadvertently alter the onset and peak characteristics of the short-acting dose. D. Inserting the needle at a 15° angle is incorrect for subcutaneous insulin administration and is more appropriate for intradermal injections. Insulin must be deposited into the fatty subcutaneous tissue, typically at a 45° to 90° angle depending on the patient's body mass and needle length. A 15° angle would likely result in an ineffective intradermal delivery, leading to unpredictable absorption rates.