In which of the following situations, is a barrier to entry into a monopoly least likely to exist?

a. A large firm enjoys economies of scale.
b. The tariffs on foreign goods are eliminated by the government.
c. A company is the sole inventor of what it produces and no one else can make a good substitute.
d. Government restrictions such as license requirements are enacted.
e. A company is the only owner of an essential resource needed to produce its product.

b