Concept: Opportunity cost is the value of the next best alternative that is given up when a choice is made.
Explanation: When a worker decides to attend university, they must give up the income they would have earned from working during that period.
Tuition, fees, and books are direct expenses, but they are not the next best alternative forgone.
Similarly, boarding, lodging, transportation, and entertainment are extra costs, not the opportunity cost.
The true opportunity cost is the wages sacrificed, because that is the alternative use of the worker's time and effort.
Thus, the decision to study means losing the salary that could have been earned instead.
Answer: C. the wages given up to attend the university