Which of the following situations is a natural monopoly? (Check all that apply.) Multiple answers:
a One company owns almost all available bauxite (the mineral needed to produce aluminum). b The U.S. Postal Service is given the exclusive right to deliver first-class mail. с The only electricity supplier in a region experiences diseconomies of scale. d One water supplier in a city can provide its service at a lower average cost than two or more suppliers could.
