The opportunity cost of Kendra choosing to go to Abby's house to watch a movie is the difference in value to Kendra of the two options. This means that the opportunity cost is the value or enjoyment she would have gained from going to Samuel's house to play board games instead of going to Abby's house. Opportunity cost refers to what is foregone when making a choice, so the correct answer is:
The difference in value to Kendra of the two options.