The correct answer is the 16th Amendment, which allowed for the implementation of a federal income tax. This had a major impact on the economy by providing the government with a new source of revenue. The Pure Food and Drug Act and the new Interstate Commerce Commission laws also had important impacts on industry and consumer protection, but the 16th Amendment had a broader economic impact. The Wisconsin Idea, while an important reform movement during the Progressive Era, did not directly impact the economy on a national level.
