The answer is C. Conflict
Sybolism is foreshadowing or details that usually remain hidden to the chracters and are only understood by the reader.
Setting is the place the story takes place
Plot is the story as a whole. The driving force that brings the character from the first page to the last.
Conflict is the main problem that can usually be singled out, that causes the main charcter to do something.
Example: In the Hunger Games, The conflict for Katniss was when Primrose was chosen to particapate in the Games. If that hadn't happened, Katniss would not have volunteered in her place and there would be no story