It is D. The American Civil War was an extended battle engagement fought between the Confederacy and the Union in the nineteenth century.
The answer is B because it the commas are used for short pauses.
I believe the answer is B. Not.
a conjunction is a word that connects sentences, phrases, or clauses. The words "but", "yet", and "so" all do that, and therefore, are conjunctions. The only word that isn't a conjunction is "not", so the answer is B. Hope that helps!