21Which of the following statements are true? (There are multiple correct answers) In the E-R diagram for OE/S, SHIPMENTS generate the SALES_INVOICES. A customer acknowledgement is sent to the customer to notify him or her of the order's acceptance and the expected shipping date. The OE/S process sends the sales order notification to the billing department to notify them of a pending shipment. A customer acknowledgement is sent to the billing department to notify them of a pending shipment. In the E-R diagram for OE/S, SALES_ORDERS activates the STOCK_PICK. If a customer refuses to accept a back order, then the sales event is terminated and the sales order is accepted.