Final answer:
The nurse's best response would be option d, stating that they are glad the patient has made progress and helped, but they cannot accept the gift.
Step-by-step explanation:
The nurse's best response in this situation would be option d: "I'm glad you've made progress and that I helped, but I cannot accept the gift."
This response acknowledges the patient's progress and expresses gratitude, while also following the agency's policies and procedures. It is important for healthcare professionals to maintain professional boundaries and avoid accepting gifts from patients to prevent any potential ethical conflicts.