During the introduction of the novel, the characters and plot are still being developed. The reader is not ready to know the conflict, as he/she has no background information to help him/her understand the impact of said conflict.
This being said, it cannot be the end of the story, as the novel must have a conflict to be written off of. To keep the readers engaged, the must know the conflict, and learn more about it throughout the story.
After eliminating those two options, we know it must be the middle of the story. It gives the readers enough time to understand what will happen in the novel, while still introducing the conflict early enough for the readers to continue reading the book.
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