12. An airport recently began offering free WiFi. Initially, only a few people use the service. At that point, what type of good is free WiFi? Later, as more people use it, connection speed slows down. At that point, what type of good is free WiFi?
(A) Initially a club good; later a public good.
(B) Initially a common resource; later a public good.
(C) Initially a public good; later a club good.
(D) Initially a public good; later a common resource.