The correct answer is C) the negative side asks follow-up questions.
The next step of the Lincoln-Douglas debate structure after the affirmative side presents their case is "the negative side asks follow-up questions."
The Lincoln-Douglas debates were a series of political debates held by the candidates to the Senate in the state of Illinois in 1858. During their electoral campaign, these two candidates debate seven times in different places. Abraham Lincoln represented the Republican party, meanwhile, Stephen Douglas represented the Democratic party. The constant topic of the seven debates was the issue of slavery, as in that time, Illinois was a free state.