Which of these is likely not a reason the natural rate of unemployment rose in the United States from 1930-1980?

Group of answer choices

Improvements in communication technologies like telephones going from presence in 30% of households to 90%

The increasing strength of labor unions in a larger fraction of the labor force post WWII

The introduction of social safety net programs like Social Security, Medicare and Medicaid, and AFDC (Cash Income Redistribution)

The top marginal income tax rising from 30% to as high as 94%