Which one of the following is the extra cost to third parties resulting from the production of another unit of a good or service? a. Research paradigm cost O b. Descriptive Research cost c. Interpretivist cost O d. Marginal external Cost Which one of the following must exists for a perfectly competitive market system? O a. All productive resources are privately owned b. Resources are mobile and may be freely employed in any enterprise OC. All relevant information is freely available to buyers and sellers Od All these choices