Which Statement Is Most TRUE About the Impact of Unions

Which statement is most TRUE about the impact of unions on wage levels in the Untied States?

A) Unions have had no impact on the wage levels of their workers.
B) Unions have tended to increase the hourly wage rates of their members relative to nonunion workers by an average of about $2.25.
C) Unions have contributed to increased income inequality in the United States by raising corporate profits.
D) The union/nonunion wage differential tends to decrease during a recession.