Well an expository essay is a writing peice that explains your topic or whatever you plan to write about and when you write you can really use any method but it has to sound right and feel right.
Therefore implies that something is occurring as a result of something else. As a result, therefore best implies a cause and effect structure.
B is the answer because it exemplifies how the word is linked with the source of where the word came from and what it means in Greek.
