Answer:
b. He is retiring, so he no longer has a trade-off of missing practice or a game
Step-by-step explanation:
First thing to establish is that the question is about seeing how an opportunity cost will have the decision of the pro-footballer on whether to move by himself or hire someone else.
As such, the opportunity cost (benefit foregone from an alternative) of moving on his own would usually mean to miss a practice or a game. In other words, the reason why he would have hired someone else in the first instance is so that he will not miss out of matches or practices.
If this assumption is followed, therefore, the best alternative is b. He is retiring, so he no longer has a trade-off of missing practice or a game.
Meaning, moving on his own will have no effect on his training or games since he is retiring.