Answer: The correct answer is "B. increase productivity but increase unemployment.".
Explanation: Efficiency salaries is a theory that says that some companies voluntarily offer salaries above the equilibrium level and this results in an increase in the productivity of their workers. As a negative issue, they can cause higher unemployment rates, since with salaries above the equilibrium salary, there is a consumer surplus. In addition, it would reduce the demand for more workers, as they have become more expensive.