Question: Classify the following as a government-enforced barrier to entry, a barrier to entry that is not government enforced, or a situation that does not involve a barrier to entry.
a. A city passes a law on how many licenses it will issue for taxicabs
b. A city passes a law that all taxicab drivers must pass a driving safety test and have insurance
c. A well-known trademark
d. Owning a spring that offers very pure water
e. An industry where economies of scale are very large compared to the size of demand in the market