The correct response is:
According to the Missouri Compromise, Kansas and Nebraska should have been free territories.
This is because the Missouri Compromise established a line that determined which territories were free and which were slave. Kansas and Nebraska were located north of that line, meaning they were expected to be free territories according to the earlier agreement. The Kansas-Nebraska Act, which allowed voters to decide the issue of slavery, undermined the Missouri Compromise, causing anger among anti-slavery Northerners.