Which of the following is not correct? Select one: a. When a union is present in a labor market, wages are determined by the equilibrium of supply and demand. O b. Like any cartel, a union is a group of sellers acting together in the hope of exerting their joint market power. O C. The process by which unions and firms agree on the terms of employment is called collective bargaining. O d. Most workers in the U.S. economy are not members of a union