Final answer:
Calling 911 is the appropriate first-aid response if a second-degree burn is larger than 2 to 3 inches.
Step-by-step explanation:
An appropriate first-aid response if a second-degree burn is larger than 2 to 3 inches would be to call 911. A burn of this size could be considered a significant injury and may require medical attention. It is important to seek professional help in order to ensure proper treatment and to prevent any complications.