The kansas-nebraska act nullified the missouri compromise by
a: abolishing slavery in all states
b: allowing slavery in all states
c: ending slavery in agreed-upon slave territories
d: allowing slavery's spread to areas that had been free for more than 30 years

It was d. allowing slavery into states that have been free for 30 years.  The act made the citizen choose for themselves about the slave issue. This upset the balance between Free State and slave state. Eventually this event would result in the Civil War.

this question makes no sense dude