I would say sorrowful due to the context, however difficult would also make sense. As it is referring to the fault as his downfall I would stick with 'sorrowful' as the answer.
D: prologue is not even a necessity so no
C: that is important but if you don't have it other people can come up with something based on your story
B: Correct grammar is definitely important
A: without plot there is nothing so i would say This is the correct answer since all the other choices rest on the play having a plot
A. In the next match, 7–7 wrestlers’ results drop below their predicted percentage.