Fill in the missing information.

a$.$ The vendor ships the inventory and sends a$($n$)$ back to the purchaser.

b$.$ After approving all documents, the purchaser sends a$($n$)$ to the vendor.

c$.$ When ordering merchandise inventory, the purchaser sends a$($n$)$ to the vendor.

d$.$ The purchaser receives the inventory and prepares a$($n$)$