Answer: the value of the best opportunity a student gives up to attend college
Explanation: Opportunity cost is the cost of loosing benefits that one could have received if he or she would have chosen one alternative over the other. Usually the chosen alternative is the best and the rejected one is the second best.
Therefore, if a student decides to get to college the other opportunities that he might have chosen like doing a job or business is his opportunity cost.
Hence from the above we can say that the right option is B.