In the Context of Incentives Given by a Producer to a Reseller's

In the context of incentives given by a producer to a reseller's salespeople,a spiff is considered legal only if:

A) the producer's goods are sold on credit.
B) customers approve of the incentive structure.
C) the reseller approves of the incentives,and it is offered to all the reseller's salespeople.
D) a salesperson engages in resale price maintenance.
E) the reseller includes the incentives in the selling cost of the product.