In discussions of barriers to entry, what is meant by the term "virtuous cycle"?

Select one:

a.A virtuous cycle refers to a firm using the profits from a monopoly in one market to establish a monopoly in another market.

b.A virtuous cycle refers to the situation where the pursuit of self-interest in establishing an entry barrier leads to an increase in social welfare (the "invisible hand").

c.A virtuous cycle refers to a situation where if a firm can attract enough customers initially, it can attract additional customers because its product's value has been increased by other customers using it, which attracts even more customers.

d.A virtuous cycle refers to successful research and development that leads to information that is used to develop other new products.