Choice "D" is correct. Shipping documents and receiving reports are internally-generated evidence, since they are created by the client rather than received from independent sources outside the enterprise.
Choice "a" is incorrect. Customer purchase orders and bank statements are both external evidence, since they are received from independent sources outside the enterprise.
Choice "c" is incorrect. Vendor invoices and packing slips are both external evidence, since they are received from independent sources outside the enterprise.
Choice "b" is incorrect. Bills of lading and accounts receivable confirmations are both external evidence, since they are received from independent sources outside the enterprise.