What Is Not Correct About the Northern U

What is not correct about the Northern U.S. abolitionist movement?

A) Northern slaveholders could sell their slaves to the south.
B) Slave owners in the North suffered significant economic loss because slaves were given their freedom much sooner than in the South.
C) Most Northern states freed slaves after they had reached a minimum age.
D) In most northern states freedom was granted over a gradual period of time.