A nurse is preparing to administer 5 units of regular insulin and 20 units of NPH insulin to a client who has type 1 diabetes mellitus. Which of the following actions should the nurse take first?

Inject 20 units of air into the vial of NPH insulin.

Inject 5 units of air into the vial of regular insulin.

Withdraw 20 units of NPH insulin from the vial.

Withdraw 5 units of regular insulin from the vial.