Unions tend to increase the disparity in pay between insiders and outsiders by ?

A. increasing the wage in the Unionized sector, Which may create a decrease in the supply of workers in the non-unionized sector
B. Increasing the demand for workers in the Unionized sector
C. decreasing the demand for workers in the Unionized sector
D. Increasing the wage in the Unionized sector which may create an increase in the supply of workers in the non-unionized sector