Final answer:
The best detail to add is information indicating an increased number of African American voters after the Voting Rights Act of 1965, as it demonstrates the removal of voting barriers.
Step-by-step explanation:
The student asked what kind of detail could be added to an article to support the author's point that the March on Washington resulted in removing barriers for African American voters. To support this point, the most effective detail to add would be information that shows an increased number of African American voters after the passage of the Voting Rights Act of 1965. This would directly illustrate the impact of the legislation on voter turnout among African Americans, evidencing that the barriers they previously faced had been diminished. Providing statistics on voter registration and participation rates before and after the Act's passage would effectively demonstrate this change.