The correct answer is (C) antislavery advocates .
In the Gettysburg address, Lincoln reminds the people that "the nation was conceived in liberty, and dedicated to the proposition that all men are created equal", meaning abolishment of slavery. In "Letter To His Son" by Robert E. Lee, he is showing his support for the Union "... but I can anticipate no greater calamity for the country than a dissolution of the Union" making him an antislavery advocate as well.