The four kinds of monopolies are: Natural, Government, Geographical, and Technlogical.
Natural: Telephone lines or Airlines.
(Hard to start own company)
Government: Postal System.
(Government created monopoly, competition is prohibited by law)
Geographical: Gas station in the middle of the Sahara desert
(Location effects potential profit, meaning people must go there for good/service)
Technological: Actual Transformers
(Company that makes something innovative has copyright or form of patent,
they have a legal monopoly over all other competitors.)