Answer:
B. People face trade- offs
Step-by-step explanation:
The given scenario points towards the principle of opportunity cost.
Opportunity cost refers to the benefits foregone of not taking up one activity when another activity is taken up instead.
The time Juanita opts to go for swimming, cannot be used for other two activities. This further implies that if one activity is to be taken up at a time, time available for pursuing other activities is getting reduced or sacrificed. The hours spent on swimming represent the hours foregone which could have been used either for biking or running.
This represents a trade off which has to be made as to decide which activity to pursue for a given time in exchange of other activities which one opts to give up (sacrifice).