If You Decide to Go to Cancún with Your Friends

Multiple Choice

If you decide to go to Cancún with your friends during spring break, you cannot go to Paris with your sister in the summer. This statement best represents this economic concept:

A) The real cost of something is what you must give up to get it.
B) "How much" is a decision at the margin.
C) People usually exploit opportunities to make themselves better off.
D) There are gains from trade.