Which of the following is a barrier to entry?

A) patents and licenses
B) buyers' incomes
C) close substitutes
D) diminishing marginal returns

Patents and Licenses

Legal mechanisms that grant inventors exclusive rights to their inventions, and permissions required to engage in certain activities or businesses.

Barrier to Entry

Economic, procedural, regulatory, or technological conditions that obstruct or restrict new competitors from easily entering an industry or area of business.