Economists use economic models to replicate real life situations for economic policy. Production possibilities frontier is one of the few economic models used to explain the behavior of economies. You are supposed to use a production possibilities frontier to show society's trade-off between two "goods" - a clean environment and the quantity of industrial output. What factor do you think determines the slope of the frontier? Illustrate what happens to the frontier if engineers develop a new way of producing electricity that emit lesser pollutants.