Given the task definition and input, reply with output. 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.

Sentence1: Billy had a toy ball. Sentence2: He would take his ball wherever he went. Sentence3: One day, he had to go to school. Sentence4: His mom took his ball away from him.
Billy was very upset.