The following sales procedures were encountered during the annual audit of Marvel Wholesale Distributing Company: Customer orders are received by the sales order department. A clerk computes the approximate dollar amount of the order and sends it to the credit department for approval. Credit approval is stamped on the order and sent to the accounting department. A computer is then used to generate two copies of a sales invoice. The order is filed in the customer order file. The customer copy of the sales invoice is held in a pending file awaiting notification that the order was shipped. The shipping copy of the sales invoice is routed through the warehouse, and the shipping department has authority for the respective departments to release and ship the merchandise. Shipping department personnel pack the order and manually prepare a three-copy bill of lading: The original copy is mailed to the customer, the second copy is sent with the shipment, and the other is filed in sequence in the bill of lading file. The sales invoice shipping copy is sent to the accounting department with any changes resulting from lack of available merchandise.
A clerk in accounting matches the received sales invoice shipping copy with the sales invoice customer copy from the pending file. Quantities on the two invoices are compared and prices are compared to an approved price list. The customer copy is then mailed to the customer, and the shipping copy is sent to the data processing department. The data processing clerk in accounting enters the sales invoice data into the computer, which is used to prepare the sales journal and update the accounts receivable master file.
She files the shipping copy in the sales invoice file in numerical sequence.

Required
a. To determine whether the internal controls operated effectively to minimize instances of failure to post invoices to customers' accounts receivable master file, the auditor would select a sample of transactions from the population represented by the
(1) Customer order file.
(3) Customers' accounts receivable master file.
(2) Bill of lading file.
(4) Sales invoice file.
b. To determine whether the internal controls operated effectively to minimize instances of failure to invoice a shipment, the auditor would select a sample of transactions from the population represented by the
(1) Customer order file.
(2) Bill of lading file.
(3) Customers' accounts receivable master file.
(4) Sales invoice file.
c. To gather audit evidence that uncollected items in customers' accounts represented existing trade receivables, the auditor would select a sample of items from the population represented by the
(1) Customer order file.
(2) Bill of lading file.
(3) Customers' accounts receivable master file.
(4) Sales invoice file.*