Final answer:
The best nursing action when an 8-year-old girl asks about a blood pressure apparatus is to give a simple, age-appropriate explanation.
Step-by-step explanation:
When an 8-year-old girl asks about how the blood pressure apparatus works, the most appropriate nursing action is to offer a simplified explanation using age-appropriate language. This explanation might include saying that the device has a special cuff that fills with air to give the nurse or doctor an idea of how strong her heart is pumping blood. It's like giving the arm a little hug to listen to the heartbeat and see how well it's working.