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: Mark and Frank were swimming in Mark's family's pool. Sentence2: Mark's mother brought out a sponge ball to them. Sentence3: Mark and Frank had fun tossing the ball back and forth. Sentence4: But then the saturated ball accidentally hit Mark's mother!
Mark and Frank apologized profusely.