I believe the answer is C. Replace they with he or she.
What are those pink things over there? This is our last chance to do the right thing. somebody call 911! I've got to say: I'm feeling pretty proud of myself right now. you have no idea who you're messing with. Just who do you think you are?
The Main Character is part of the story
I'm guessing this is about George Orwell's book. It's a science fiction novel because of the Thought Police and telescreens. We don't have any of those, and the novel is pretty futuristic in those ways. Hope this helps!
One way to vary the syntax of the text is to combine sentences since, in this way, your structures will be longer and more complex to follow. This could be done by means of links such as: however, in addition, therefore, etc. When using these words, you create semantic relations between the syntactic structures and make the reading process more difficult because, as I've I said, sentences become longer and therefore the reader has to keep more information in mind to follow the train of thought.
You could also vary the syntax by adding phrases or clauses. This option is similar to the previous one since it also refers to the complexity of the syntactic structures of the text.