Answer:
D. developed a theory of biological racial superiority to justify slavery.
Step-by-step explanation:
The economy of the Southern States was dependent on the slave labor, which was vital for the white population who controlled large tracts of land. But a major problem to justify slavery was solved by the scientific racism or biological racial superiority through which it portrayed that it is scientifically proved that the white race is superior to the race of colored people. Therefore it was installed in the minds of large slave population that they are born to serve their masters.