An Important Unanswered Question About the Role of Unions in Developed

An important unanswered question about the role of unions in developed economies is whether the presence of unions affects long-run productivity.There is some evidence to suggest that the presence of a union

A) increases the human capital of unionized workers,which leads to increased long-run productivity for the firm.
B) reduces the demand for labour and therefore the demand for physical capital.
C) decreases the human capital of unionized workers,and therefore reduces long-run productivity.
D) reduces the level of employment (because of the union-wage premium) and thus raises the marginal product of labour.
E) reduces the expected profitability of installed capital and therefore leads to reduced capital investment by firms.