It Is Legitimate for a Manufacturer to Charge a Retailer

It is legitimate for a manufacturer to charge a retailer a lower price than its usual price if:

A) the retailer is related to the seller.
B) neither the retailer nor the seller are publically-traded companies.
C) the seller is trying to match a competitor's price.
D) the different price is a one-time occurrence.
E) the difference between the regular price and the reduced price is less than or equal to ten percent.