Which Scenario Best Exemplifies the Concept of Opportunity Cost

Which scenario best exemplifies the concept of opportunity cost?

A) Arthur has been offered a promotion to department manager. The promotion means more hours at work and more responsibilities, but includes only a title change and not an increase in salary.
B) Louisa has a small bakery that generates a modest profit for her. She knows if she pools her profits for two years she will have enough money to expand her bakery and increase her profits.
C) Bernardo has been offered a chance to invest in a startup company that has the potential to generate a great deal of profit if it is successful. Since the cost to invest is very high, he must decide if the potential profit is worth the risk.
D) Beth has enough money to either buy her son a new pair of jeans before winter or get him vaccinated against the flu. She knows that once she chooses one alternative, she will be unable to afford the other.