Concept:The production possibility curve illustrates scarcity, opportunity cost, and efficiency, but it does not illustrate risk.
Explanation:The PPC shows scarcity because it sets a limit on what can be produced with available resources and technology.
It shows opportunity cost because producing more of one good means giving up some of another good.
It also shows efficiency because points on the curve represent the full and best use of resources, including allocative efficiency.
Risk, however, involves uncertainty about future outcomes.
The PPC assumes known resources and fixed technology, so it does not deal with risk.
Answer:A. Risk