The opportunity cost in this scenarlo is that "Later on, his friend Theo Informed him about a surprise birthday party for another friend. Theo plans to reserve a room at a restaurant for the celebration, with the cost to reserve the room spilt between Theo, Harry, and three other friends."
This refers to the cost of not being able to do other things with time and resources because of doing the chosen activity.
In this question context, the opportunity cost exist when "Later on, his friend Theo Informed him about a surprise birthday party for another friend. Theo plans to reserve a room at a restaurant for the celebration, with the cost to reserve the room spilt between Theo, Harry, and three other friends."
Therefore, the Option D is correct.
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