Choice "C" is correct. Comparison of daily sales summaries to daily postings to the accounts receivable ledger would ensure the completeness of the accounts receivable ledger.
Choice "a" is incorrect. Comparison of sales invoices to shipping documents verifies occurrence of the sale, not completeness of the accounts receivable ledger.
Choice "d" is incorrect. Reconciliation of the accounts receivable ledger to the general ledger would not assure the accuracy and completeness of the accounts receivable ledger because a sale which was improperly excluded from receivables would likely be omitted from both ledgers.
Choice "b" is incorrect. Ensuring that all shipments are billed verifies completeness of sales transactions, but does not provide evidence that all sales are recorded in the accounts receivable ledger. In other words, the fact that a shipment was billed does not mean that the invoice was also recorded in the accounts receivable ledger.
