If Perkston's Aquatic Store,a Retailer of Aquarium Fish and Supplies,buys

If Perkston's Aquatic Store,a retailer of aquarium fish and supplies,buys one 200-gallon fish tank from Merida's Aquarium Products,it will be billed $329.If it buys more than six during the upcoming year,it will get a 20 percent discount on each aquarium.This savings is referred to as a:

A) cumulative discount.
B) promotional allowance.
C) trade discount.
D) functional discount.
E) single-order discount.