I narrowed it down to B and D. Going to say D though
Answer: a. Such a class you must have, or you would not have that other class which leads progress, civilization, and refinement.
Explanation: An analogy is a comparison between the features of two or more things, analogies are often used to help explain a point the view or an argument about any topic. In the given excerpt from James Henry Hammond’s speech “Cotton Is King” the piece of text that uses an analogy to justify the existence of the institution of slavery is the one from option a, it compares the "class" of slaves with the progress, civilization and refinement.
1.) Mary
2.) continent
3.) laying
4.) obtuse
