b$.$ The local river has so much pollution that three$-$eyed fish are forming. Regulations are therefore enacted to limit the amount of chemicals dumped into the river.

c$.$ At a high$-$end restaurant, the restaurant owner has one chef at a meat station, one chef at a vegetable station, and one chef, who has an artistic eye, plate the food she is given. The result is increased service speed, enabling the kitchen to serve more customers in an evening.

d$.$ During the summer, a bumper crop of oranges in Florida causes a surplus in the supply of oranges nationwide. As a result, prices fall to compensate for the surplus, and consumers enjoy the fruits of the farmers' labor.