Final answer:
Sending a written request to entity's customers to report the amount owed is known as External Confirmation, used in auditing to verify receivables accuracy.
Step-by-step explanation:
The act of sending a written request to the entity's customers requesting that they report the amount owed to the entity is known as a) External Confirmation. This process is used in auditing to verify the accuracy of accounts receivable records. An external auditor will send a confirmation letter to the customers asking them to confirm directly the balance they owe to the company. The customers' responses provide a third-party verification of the receivables stated in the financial statements, ensuring their accuracy and legitimacy.