The correct approach to reconcile a bank service fee listed on the statement is:
B. Enter it into your external register in the same manner as a withdrawal.
This ensures that your records reflect the accurate balance and account for the fee appropriately. Erasing it from the bank statement (option A) is incorrect as it would misrepresent the bank's records, and keeping a separate diary of service fees (option C) is not a practical way to maintain an accurate record of all transactions.