An audit team is auditing sales transactions. One step is to vouch a sample of debit entries from the accounts receivable subsidiary ledger back to the supporting sales invoices. The purpose of this audit procedure is to establish that
a. Sales invoices represent bona fide sales.
b. All sales have been recorded.
c. All sales invoices have been properly posted to customer accounts.
d. Entries in the accounts receivable subsidiary ledger were properly invoiced.