A Supermarket Offers a 1-Litre Milk Carton, a 2-Litre Milk

A supermarket offers a 1-litre milk carton, a 2-litre milk carton, and a 3-litre milk jug at $3.50, $6.00, and $9.00, respectively.Thus, the larger the quantity bought, the lower the cost.This is an example of a:

A) rebate.
B) size discount.
C) markdown.
D) coupon.
E) quality discount.