Final answer:
The nurse should advise Mario to use a pillow to apply pressure against the incision, a method known as splinting, which can help to minimize pain during exercises that increase pressure on the incision site.
Step-by-step explanation:
The best response by the nurse to Mario, who complains of mild incisional pain while performing deep-breathing and coughing exercises, would be option C: "With a pillow, apply pressure against the incision." This technique is known as splinting, and it is a common practice used to help patients manage pain after surgery, especially during activities that increase pressure on the incision site, such as coughing or deep breathing. Recommending splinting can help Mario to minimize pain and support the healing process. It's also important for the nurse to consider other options, such as providing pain medication if it's deemed necessary and instructed by the physician.