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: Debra's twins had talked about building a sand castle for a week. Sentence2: She decided to surprise them with a trip to the beach on her day off. Sentence3: She purchased plastic pails of different sizes to act as molds. Sentence4: Debra taught them to fill a pail with sand to flip them carefully.
They took pictures of the castle for their scrapbook when it was done.