Critically evaluate each of these statements:
a. “The relative decline of the American labor movement can be explained by the shift from goods-producing to service providing industries and by the closely related shifts from blue- to white-collar occupations and from male to female employees.”

b. “The success of unions in raising their wages relative to nonunion workers has contributed to the decline of unionism.”
c. “Unionized firms have tended to become less profitable and, therefore, employers are more resistant to unionization.”