Final answer:
Excess competition is not a reason that monopolies arise; it actually prevents monopolies by increasing the number of competitors in the market. Monopolies typically form due to economies of scale, control of natural resources, and patents.
Step-by-step explanation:
The question 'Which of the following is not a reason that monopolies arise?' relates to the concept of how monopolies form, focusing on barriers to entry. The correct answer is B. excess competition. Monopolies typically arise due to factors such as economies of scale, which can lead to natural monopolies when one firm can supply the market more efficiently than multiple firms; or control of natural resources, where a firm may dominate a market due to exclusive access to a crucial resource. Patents are a form of legal protection that grants a company a monopoly on the use and development of an invention for a certain period. Excess competition, on the other hand, typically reduces the potential for monopoly because it implies that there are many competitors in the market, preventing any single firm from having significant market power.