Final answer:
The nurse should plan the priority intervention of maintaining a structured routine and minimizing stimulation.
Step-by-step explanation:
In caring for a child with autism spectrum disorder (ASD) who is admitted to the hospital with pneumonia, the nurse should plan the priority intervention of maintaining a structured routine and keeping stimulation to a minimum (option a). Children with ASD often thrive in structured environments and may become overwhelmed or agitated by excessive stimulation. By maintaining a structured routine and minimizing stimulation, the nurse can help create a calm and predictable environment for the child, which can facilitate their recovery.