The solid line in the saw$-$tooth graph shown below depicts the inventory level for an item controlled by a fixed$-$orderquantity inventory system. Which letter $($A$-$E$)$ describes the order quantity? You may need to use the scroll bar on the bottom of the page to see the entire diagram.

Inventory Level

Select one:

a$.$ letter $C$

b$.$ letter $A$

c$.$ letter B

d$.$ letter $E$

e$.$ letter D