Vac "N' Sew Will Give Customers $100 for a Used

Multiple Choice

Vac "N' Sew will give customers $100 for a used vacuum cleaner,regardless of condition,when they purchase a new vacuum or sewing machine.This essentially reduces the price by $100.What is this type of discount called?

A) functional discount
B) captive product discount
C) seasonal discount
D) trade-in allowance
E) by-product allowance