Answer:
B: The net profit of installing the garage.
Step-by-step explanation:
The opportunity cost is the next best thing that you could be doing but chose to give up in order to do something else. For example, if I chose to spend the day studying for a test, I won't have as much time to watch cat videos, hang out with my friends, or work on the website I'm coding. Since I love coding more than anything in the world, the time I could've spent coding is the opportunity cost of choosing to study.
A and C can be safely eliminated because they are describing the business expenses of the contractor, not what they could be missing out on if they choose to renovate the bathroom. In this case, D wouldn't make any sense since they wouldn't be missing out on any profits from the bathroom project at all. Therefore, the correct answer is B. The contractor can't be in two places at once, and by choosing the bathroom, they're passing up the opportunity to work on the garage and any resulting profits.