Definition: In this task, you're given a four sentences of story written in natural language. Your job is to complete end part of the story by predicting appropriate last sentence which is coherent with the given sentences.
Input: Sentence1: Bob was at the grocery store. Sentence2: At check out, he realized he forgot his credit card. Sentence3: The woman behind him offered to buy his groceries. Sentence4: Bob was so appreciative.

He promised to pay her back.