A nurse is preparing regular and NPH insulin in the same syringe for a client who has diabetes mellitus. Which of the following actions should the nurse take?

Shake both insulin vials for 2 min before withdrawing the doses.

Administer the mixture within 5 min of preparing it.

Withdraw the NPH insulin before the regular insulin.

Inject air into the regular insulin vial before injecting air into the NPH vial.