Ana is training for a triathlon, a timed race that combines swimming, biking, and running.

Consider the following sentence: In order to swim for an hour, Ana must take time away from work, where she earns $10 per hour. This is in addition to paying a $4 entrance fee for the pool.

Which basic principle of individual choice do these statements best illustrate?

The cost of something is what you give up to get it.

People usually exploit opportunities to make themselves better off.

Trade can make everyone better off.

Markets are usually a good way to organize economic activity.