Patents a. always increase total welfare. b. are a form of trade secret. c. reduce deadweight loss. d. create monopoly power.

Creates monopoly power

Explanation: A patent can be defined as an intangible asset the gives its holder the right that no other person in the world can use, sell or produce the unique good or service that has been patented by its inventor.

Thus, the right to produce or use a specific invention by a single person can lead to monopoly in that particular industry.

Hence from the above we can conclude that the right answer is option D.