Final answer:
Barriers to entry can be government-enforced, non-government-enforced, or situations that do not involve a barrier. Examples of barriers to entry include patents, trademarks, copyrights, control of physical resources, and legal restrictions on competition. Technology, advertising, and patents are examples of barriers to entry, while income is not.
Step-by-step explanation:
Barriers to entry prevent or discourage competitors from entering the market. These barriers include: government-enforced barriers such as legal restrictions on competition; non-government-enforced barriers such as intellectual property protection and control of a physical resource; and situations that do not involve a barrier to entry like an industry where economies of scale are very small compared to the market demand.
In the given options, technology is an example of non-government-enforced barrier to entry, as it can be used to create innovative products that give a company a competitive advantage. Advertising can also be a non-government-enforced barrier as it helps in building brand awareness and reputation. Patents are a form of government-enforced barrier that grant exclusive rights to an invention. Lastly, income is not a barrier to entry but rather a measure of the financial resources available to potential market entrants. Therefore, the answer is income.