Answer:
B. the highest valued alternative that must be given up to engage in an activity.
Explanation:
Opportunity Cost is the cost of next best alternative foregone while choosing an alternative.
Eg1: If I like Chapati more than rice & rice more than curd, the opportunity cost of consuming chapati is the next best option i.e rice.
Eg2 : Working as school teacher with salary 20000, next best option salary as coaching tutor i.e 10000 is the Opportunity Cost
A is inapt : Opportunity cost can be monetary or non monetary. Eg2 has monetary opportunity cost. But, Eg 1 has opportunity cost in terms of rice' (sacrifised) satisfaction.
C is inapt : Opportunity cost is only the cost of next best alternative & not all alternatives. Eg1 - Curd i.e 3rd best option after chapati, is not the opportunity cost after chapati.