The answer is A, cause/effect. Marcia is focusing on how the war started, what ended it, and how it affected America. Cause/effect covers all these things, while the other answers either skip over these things completely or concentrate on only a few.
        
             
        
        
        
I think it was The Norman conquest, but i’m not sure!
        
             
        
        
        
C.
The introductory phrase, "Crowned with a wreath of olive leaves", is correctly separated by a comma.