Answer: C. opportunity cost
In economics, "opportunity cost" is the value of something that is given up in order to acquire something else. There are always multiple uses for capital (cash or money for investment), as well as other economic resources (labor, land, etc). So we're always faced with opportunities and make decisions about which opportunities we'll pursue and which we'll not pursue. The concert tickets are an opportunity cost that Benjamin decided against in order to purchase jeans instead.