A transaction processing system interfaces with the general ledger. Data analytics has identified that some transactions are being recorded twice in the general ledger. While management states a system fix has been implemented, what should the IS auditor recommend to validate the interface is working in the future?

A. Perform periodic reconciliations.
B. Ensure system owner sign-off for the system fix.
C. Conduct functional testing.
D. Improve user acceptance testing (UAT).