How is a stolen ATM/debit/check card entered into the system?

A stolen ATM/debit/check card is entered into the system using transaction EA. This transaction signifies that a card has been reported as stolen and needs to be flagged in the system for monitoring and preventing unauthorized transactions. By entering the information through this specific transaction, the system can update its records effectively, ensuring that the card is recognized as compromised.

The other options do not pertain to the standardized entry process for stolen cards. For instance, transaction AA is typically used for authorizations rather than reporting theft. Transaction ST does not specifically denote the action of reporting a stolen card, and transaction STOLEN, while it sounds relevant, is not a standard or recognized transaction code in this context. Thus, transaction EA is the correct choice, as it aligns with the specific protocol for handling stolen card reports.