Which of the Following Is an Example of a Social

Which of the following is an example of a social exchange rather than an economic exchange?

A) A coworker negotiates two days of vacation time next month to make up for working over the weekend.
B) The company gives you comp time so if you work through lunch you can leave early.
C) A coworker bought office supplies for your department last month, and you buy computer supplies for his department this month.
D) A coworker helped you with ideas to finish a project last week, so you take her to lunch one day.