Explain how each of the following situations illustrates one of the five principles of interaction.

a. Using the college website, any student who wants to sell a used textbook for at least $X is able to sell it to another who is willing to pay $X.

b. At a college tutoring co-op, students can arrange to provide tutoring in subjects they are good in (like economics) in return for receiving tutoring in subjects they are poor in (like philosophy).

c. The local municipality imposes a law that requires bars and nightclubs near residential areas to keep their noise levels below a certain threshold.

d. To provide better care for low-income patients, the city of Tampa has decided to close some underutilized neighborhood clinics and shift funds to the main hospital.

e. On the college website, books of a given title with approximately the same level of wear and tear sell for about the same price.