Opportunity cost問題

Opportunity cost means the highest valued option forgone.

Based on Jone's preference, going to USA is the highest valued option. Going to China followed and going to Japan the least.

That's meant when Jone has chosen going to USA, going to China is his opp cost since it is the highest valued option forgone. Any change of opp cost occurs only when the value of opp cost changed. That's meant opp cost changed only when the value of going to China either increased or decreased. Since now, the workes of the USA Airport go on strike, all flight to USA have to be cancelled only are affecting the value of going to USA, but not affecting the value of going to China. Therefore, Jone's opp cost is still going to China.

Are you sure that this is true?
I think the second answer is more reasonable.

When going to USA is no longer an option, it is meaningless to discuss the cost of an unavailable option since opportunity cost is a forward looking concept. On the other hand, given other things constant, Jone would choose the second preferred option, i.e. going to China. If Jone doesn't choose China he will choose Japan instead according to the preference order, because going to USA is no longer an option, that is, Jone now gives up Japan for China. So new the relevant opportunity cost is the cost of going to China, which is equal to the value from the trip to Japan instead.