Read the excerpt below from the Supreme Court ruling in the Scott v. Sandford. [T]he legislation and histories of the times, and the language used in the Declaration of Independence, show, that neither the class of persons who had been imported as slaves, nor their descendants, whether they had become free or not, were then acknowledged as a part of the people.

The main subject of the excerpt is
A. the lack of citizenship for enslaved people.
B. the practice of importing enslaved people from Africa.
C. the practice of relocating from a slave state to a free state.
D. the right of an owner to retain his or her property.