Final answer:
The incorrect explanation for the decline in union membership and the number of unionized workers is 'd. The structure of American industry is stagnate', as the industry has shifted from manufacturing to service sectors, not remained stagnant.
Step-by-step explanation:
Since 1983, the number of workers in unions in the private sector and the membership rate have declined for various reasons. However, not all offered explanations for this decline are accurate. As established by economists, potential reasons include the shift from manufacturing to service industries, globalization and increased foreign competition, and the presence of workplace protection laws that may reduce the perceived need for unions. Additionally, the U.S. legal environment often presents more challenges for unions to organize workers.
Out of the choices given, "d. The structure of American industry is stagnate" is not an explanation for this decline, since the actual trend has depicted a shift in the structure of industry, from manufacturing sectors, where unions used to be strong, to service sectors, where there has been less union success. Moreover, the number of jobs in service industries and in government has dramatically increased, indicating that the industry structure is not stagnant but has evolved over time.