What caused the controversy over the addition of Missouri as a state?

a
Missouri statehood would disrupt the balance between free and slave states in Congress.
b
Fighting between pro- and anti-slavery groups made it difficult for Missouri to elect a state government.
c
Proponents of slavery feared Missouri’s proximity to free states would encourage slaves to revolt.
d
The vast majority of Americans believed adding Missouri would harm the nation’s economy.

a

Missouri statehood would disrupt the balance between free and slave states in Congress.