Which of the following is NOT an example of barriers to entry?
a.
Cable companies must lay miles of underground cable before they can serve a single customer in a new market.
b.
In some counties, laws require retail stores to be closed on Sundays.
c.
An entrepreneur wishing to own a clothing store must rent a building, hire workers, and buy clothing for sale.
d.
A person who wishes to practice medicine is required to attend medical school, complete an internship, and pass a state exam.