what is the answer to these?

17. Which document initiates the revenue cycle? a. Sales invoice b. Sales order c. Journaf vouctier d. Customer's purchase order 18. When should a customer be hilled for a back order? a. When original goods are shipped b. When the purchase order is recelved c. Customer ts not billed for back orders because a back order is a lost sale d. When back ordered goods are shipped 19. What is a receihing report weed for? a. Record receipt of goods from vendors 6. Authorize the purchasing department to order goods c. Bill for goods delivered d. Ordergoods from wendors