Questions: Walter Reuther was a leader in the early motion picture industry. organizing automobile workers. the Federal Writers' Project. opposing FDR's Court-packing plan.

The answer is: organizing automobile workers.

Explanation for each option:

1. The early motion picture industry: This is incorrect. Walter Reuther was not involved in the early motion picture industry. He was primarily known for his work in labor movements, particularly in the automobile industry.

2. Organizing automobile workers: This is correct. Walter Reuther was a prominent labor leader who played a significant role in organizing automobile workers. He was a key figure in the United Auto Workers (UAW) union and was instrumental in securing better wages and working conditions for auto workers.

3. The Federal Writers' Project: This is incorrect. The Federal Writers' Project was a New Deal program to fund written work and support writers during the Great Depression. Walter Reuther was not associated with this project.

4. Opposing FDR's Court-packing plan: This is incorrect. While Walter Reuther was active during the time of Franklin D. Roosevelt's presidency, he is not known for his stance on FDR's Court-packing plan. His primary focus was on labor rights and union activities.

In summary, Walter Reuther is best known for his leadership in organizing automobile workers, making option two the correct answer.