What Was the Significance of the Northwest Ordinance of 1787

What was the significance of the Northwest Ordinance of 1787 for African Americans?

A) It had almost no effect because huge numbers of slaves continued to live under slavery until the Civil War.
B) The ordinance set a legal and geographical precedent for limiting where slavery could and could not exist.
C) It demonstrated that the Articles of Confederation government had significant amounts of power in many areas.
D) It banned the slave trade, but not slavery, from the territory.