You will be given a definition of a task first, then some input of the task.
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: He loved all the safety features. Sentence2: He was showing it off to his friend. Sentence3: It accidentally went off. Sentence4: John was surprised.
Output:
1, John bought a new gun.