For each of the following examples, state which of these approaches is being taken to manage a common resource or supply a public good: social norms, quota, tradable allowance, government provision, or property rights. 

a. A nonprofit organization spray-paints signs on storm drains reminding everyone that it “drains to the ocean” with a picture of a fish. 

b. A city starts a free program that collects recyclable glass, paper, and plastic from residents’ doorsteps. 

c. In England, municipal-waste authorities are given a percentage of an overall limit that can be put in the landfill each year. These percentages can be traded among municipalities. 

d. American bison, which once roamed freely across the Great Plains, are now raised on ranches for commercial purposes.