Answers to English questions are usually very subjective, and your question is no exception.
I would have to say TRUE though because the plot line is more synonymous with the story in general, whereas the theme is more like the main idea/ lesson to be learned from the text.
I’m sorry if you get this one wrong, all English teachers are different and this question is very subjective. So good luck and Cheers!
Answer:
informal is the first sentence and formal is the second sentence.
The second one where it starts with Math class