The correct answer is - C. Anyone with a black ancestor was considered black.
The one-drop rule was a rule based on racial segregation. According to this rule, any individual that had at least one ancestor that was of sub-Saharan ancestry, thus black (Negro by historical terms), was considered a black person. This rule was based on racial segregation, and the attempt to maintain purity in the bloodline of the white people, by deliberately putting the people with sub-Saharan ancestry aside from the white communities.
