After Offering a Promotional Allowance, the Price of a Product

After offering a promotional allowance, the price of a product returns to its regular price level. When this happens, the retail store's gross margin on that product ________ on those items that were bought with the allowance but not sold during the price special promotion.

A) decreases, though minimally
B) increases substantially
C) remains the same
D) fluctuates wildly
E) vanishes