41. The auditor is concerned that a client is failing to bill customers for shipments. An auditor procedure that would gather relevant evidence would be to

1. select a sample of duplicate invoices and trace each to related shipping documents
2. trace a sample of shipping documents to related duplicate sales invoices
3. trace a sample of sales journal entries to the accounts receivable subsidiary ledger
4. compare the total of the accounts receivable schedule with the balance of accounts receivable in the general ledger