Which of the following best fits the description of a natural monopoly?
Tap water service has a monopoly since economies of scale make it impractical for multiple companies to place water pipes.
The US government has granted the Post Office a monopoly on the delivery of first-class mail.
Until 2016, AstraZeneca had a patent on Celestra, a cholesterol medication.
Prior to the 1940s, Alcoa had a monopoly because it controlled all of the US bauxite mines.