Explain the impact, if any, of each of the following on the production possibilities curve:
a. Europe’s population fell by 30 to 60 percent following an outbreak of bubonic plague, also known as Black Death, in the fourteenth century.
b. In the next 20 years, a sizeable proportion of the United States labor force is expected to include many people who are above the age of 65.
c. Canada recently discovered large reserves of shale gas (shale gas is natural gas that is trapped in fine-grained sedimentary rock).