In the seven lincoln-douglas debates, the number one topic was

a) states' rights

b) popular sovereignty

c) secession

d) slavery

Option D.

Explanation:

Slavery, is the right answer.

The debates between Abraham Lincoln and Stephen Douglas was known as the Lincoln–Douglas debates. Such debates were a group of seven discussions. These debates took place at the time when senators were chosen by legislatures of the states and both Lincoln and Douglas were seeking to get charge of the Illinois General Assembly for their own political parties. Though Illinois was a free state during this time the theme of all the seven debates remained Slavery.

answer; ///i believe the correct answer is john marshall;