why not C? why does the frontier shift?

Assume that an association of young workers has lobbied the government to require that all workers retire once they reach the age of fty. What impact would this law have on the nation's production possibilities frontier? A. B. C. WP no impact at all. The level of unemployment would decrease so the production possibilities frontier would shift outward. The nation would move to a new position on its production possibilities frontier but the frontier itself would not shift. The production possibilities frontier would shift inward. The number of young workers would increase so the production possibilities frontier would shift outward