On What Grounds Did Southerners Claim That Slavery Was "Modern

On what grounds did southerners claim that slavery was "modern"?

A) It was strongest in the United States, one of the most modern nations in the world.
B) It was made possible by the transportation revolution of the past two centuries.
C) It represented an innovation in securing human labor.
D) It was the foundation of the cotton economy, whose products were essential to modern life.
E) It offered to slaves the opportunity to learn to read and write.