The correct answer is coupons and comparative shopping.
Coupons are commodities that give consumers a saving on the purchase of an item(s) at particular stores. These coupons help individuals to save money. Comparative shopping works in a similar way. However, instead of having a physical coupon to show, consumers can compare prices of goods from different stores using resources like newspaper advertisements or online databases.
Opportunity costs and marginal benefits have nothing to do with saving money. Rather, these deal with other economic principles like choosing between different options and the additional satisfication that a person gets from consuming more of a good.
