Which of the following statements concerning internal control procedures for merchandise sales is not correct?

a$.$ Shipping and billing documents are prepared based on the order document.

b$.$ A sale and its associated receivable are recorded only when the order, shipping, and billing documents are all present.

c$.$ Accounting for a sale begins with the receipt of a purchase order or some similar document from a customer.

d$.$ The order document is not necessary for the buyer to be obligated to accept and pay for the ordered goods.