The correct answer is b. splitting votes from the major two political parties.
Third parties in the Progressive Era had a major impact on the U.S. political system by taking votes away from the two major parties, the Democrats and Republicans. This led to a more competitive political environment and forced major party leaders to adopt new ideas and policies to try to attract voters back to their party. Additionally, third parties brought attention to issues that were not being addressed by the major parties and helped to shape public opinion on a range of social, economic, and political issues.