The correct answer is B.
The opportunity cost is beared any time that a choice is made, and it is defined as the value of the best alternative that has been rejected when the choice is made. The alternative that meant the highest opportunity cost for an individual, would be the chosen one, in this case: saving money for the trip overseas.
Nick desired to purchase a gaming console too but, as he could not afford both options with the money of the lottery price, he has renounced to the console that constitutes the opportunity cost.