In this task, you're given four sentences of a story written in natural language in which one part is missing. Your job is to predict the position and missing part of the story and return in the following format: position, missing part. The missing part is a sentence that completes the story, and the position is the number of the missing sentence in the new story.

Sentence1: Allison decided she wanted to learn more about her area's history. Sentence2: She went down to the library to check out a book on it. Sentence3: She went inside and couldn't understand how the books were sorted. Sentence4: That helped her find what she wanted.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
4, She found a librarian who explained the dewey decimal system.