Final answer:
Option a) Security breaches. A significant concern regarding compliance issues when using RFID for large events like music festivals is security breaches.
Step-by-step explanation:
When using RFID for large events like music festivals, a significant concern regarding compliance issues is security breaches. RFID technology uses radio waves to transfer data, and if not properly secured, it can be vulnerable to hacking and unauthorized access. Organizers of large events need to implement robust security measures to protect the data stored on RFID tags and prevent any breaches.