Southern Democrats is the correct answer.
It was the issue of slavery which mainly divided US into northern and southern states and further Democratic party into southern Democrats and Northern Democrats. The Southern Democrats were pro-slavery and thus challenged the Northwest Ordinance's prohibition of slavery by the late 1850s.
The first answer would be answer c. then question 2 would be c also. the third is b
Your questions asks why the Southern Military (Confederacy) decided to defend instead of attack.
Your answer would be C). Southern leaders thought their knowledge of Southern lands would help them defeat the Union forces.
The reason why this would be the correct answer is because the South believed that their knowledge of their land would give them the advantage in winning the war. In other words, you can say that the South "played home field." The terrain in the South was different than the terrain in the North, so they used it to get the Northerners (the Union) confused when trying to attack them. The Southerners knew where everything is: all of the bases, hiding spots, etc, and used it to a certain advantage. All in all, the Southern leaders thought that the Union would be weaker on unknown territory.
They all was removed from the letter