The correct answer is e. of all of the above.
Frictional unemployment is a natural form of unemployment that occurs when people are between jobs or are entering the labor force for the first time. The reasons listed contribute to frictional unemployment in various ways:
- Efficiency wages may lead firms to pay above-market wages to boost productivity, which can create a surplus of labor, contributing to frictional unemployment.
- Minimum-wage laws can cause wage floors that prevent some workers from finding jobs, leading to periods of unemployment as they search for jobs that pay at or above the minimum wage.
- Changes in the demand for labor among different firms can cause workers to leave jobs and search for new positions, leading to frictional unemployment.
- Unions may negotiate higher wages or better working conditions, which could lead to temporary unemployment for workers who are in the process of negotiation or transition between unionized and non-union jobs.
Thus, all the factors mentioned can contribute to frictional unemployment, making "e" the best choice.