5.Market failures occur when

A. there is a change in quantity demanded.

B. there is an increase in demand.

C. economic efficiency increases.

D. externalities exist.

6. External costs can be defined as

A. the cost associated with private production, but partially borne by society.

B. the cost of providing all public goods and services.

C. the cost of running the federal government.

D. the sum of all private production