The correct answer is: Overstatement of accounts receivable.

The confirmation of accounts receivable is primarily a test for overstatement/existence of accounts receivable. It cannot be a means of testing for understatement due to omission of accounts receivable from the receivables ledger: sampling from a population cannot establish the completeness of that population because missing items could not possibly be selected for testing. It could in theory reveal omissions of invoices from the receivable accounts confirmation. But receivables may well not point out such omissions in the reply to the confirmation! In addition the testing focuses on the year-end accounts receivable and so overstatement of sales will not be confirmed.