A: If a restaurant has given you free food, you should make sure to tip them the exact amount of the cost of the free food they give you.
B: If a neighbour has helped you water your plants and check your mail while you were on vacation, you should only return that favour once.
C: If a colleague has helped you with your presentation once at work, you should help them do all their projects in the future.
D: If a friend has cooked for you multiple times, you should make sure that you cook for them a few times in the future.
