Question

an opportunity cost is the
value gained by your top choice
value of the best alternative given up
value of all alternatives given up

Explanation:

Opportunity cost in economics is defined as the value of the best - alternative forgone when a decision is made. It's not the value of all alternatives given up (which would be too broad and often unfeasible to calculate precisely) nor the value gained by the top choice.

Answer:

value of the best alternative given up