Final answer:
Frederick Douglass and William Lloyd Garrison effectively used writing and speaking against slavery as their method of civic participation, making a significant impact on public consciousness and international support for abolition.
Step-by-step explanation:
The method of civic participation that was most effective for abolitionists Frederick Douglass and William Lloyd Garrison was c. Writing and speaking against slavery. Frederick Douglass and William Lloyd Garrison effectively used writing and speaking against slavery as their method of civic participation, making a significant impact on public consciousness and international support for abolition.
They used moral persuasion and publicized the atrocities of slavery to shift public opinion. While Garrison focused on non-political strategies like his newspaper, The Liberator, Douglass utilized his skills as a powerful orator and a writer, notably through his autobiographies and lectures, to garner international support for the abolitionist cause.
Both emphasized the urgency of immediate abolition and sought to affect change through intellectual and moral appeals rather than the political process.