The following sales procedures were encountered during the regular annual audit of Marvel Wholesale Distributing Company.

Customer orders are received by the sales order department. A clerk computes the dollar amount of the order and sends it to the credit department for approval. Credit approval is stamped on the order and returned to the sales order department. An invoice is prepared in two copies, and the order is filed in the customer order file.

The customer copy of the invoice is sent to the billing department and held in the pending file awaiting notification that the order was shipped.

The shipping copy of the invoice is routed through the warehouse and the shipping department as authority for the respective department to release and ship the merchandise. Shipping department personnel pack the order and 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 invoice shipping copy is sent to the billing depart¬ ment.

The billing clerk matches the received shipping copy with the customer copy from the pending file. Both copies of the invoice are priced, extended, and footed. The customer copy is then mailed directly to the customer, and the shipping copy is sent to the accounts receivable clerk.

The accounts receivable clerk enters the invoice data in a sales journal, posts the customer’s account in the subsidiary customer accounts ledger, and files the shipping copy in the sales invoice file. The invoices are numbered and filed in sequence.

Required :

a. In order to gather audit evidence concerning the proper credit approval of sales, the appropriate sampling unit for the selection of transaction documents would be from the population represented by the:
(1) Customer order file

(2) Bill of lading file (3) Subsidiary customer accounts ledger (4) Sales invoice file

b. In order to determine whether the system of internal control operates effectively to minimize errors of failure to post invoices to the customer accounts ledger, the appropriate sampling unit for the selection of transac¬ tions would be from the population represented by the:
(1) Customer order file (2) Bill of lading file (3) Subsidiary customer accounts ledger (4) Sales invoice file

c. In order to determine whether the system of internal control operates effectively to minimize errors of failure to invoice a shipment, the appropriate sampling unit for the selection of transactions would be from the population represented by the:
(1) Customer order file (2) Bill of lading file (3) Subsidiary customer accounts ledger (4) Sales invoice file

d. In order to gather audit evidence that uncollected items in customer accounts represented valid trade receivables, the appropriate sampling unit for the selection of transactions would be from the population represented by the:
(1) Customer order file (2) Bill of lading file (3) Subsidiary customer accounts ledger (4) Sales invoice file