Answer: D. is appropriate when units are sold/used as they are produced
Explanation:
The economic production quantity model is sometimes referred to as the EPQ model and it is used to know the amount of goods or services that a company should order so that the total inventory costs can be reduced.
From the options given, it should be noted that the economic production order quantity is appropriate when units are sold/used as they are produced.
Therefore, the correct option is D.