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.
Q: Sentence1: Donna realized it was finally time to potty train her son. Sentence2: She went and bought him a training toilet and pull ups. Sentence3: She worked with him by showing him how to use the potty. Sentence4: He really struggled and didn't seem to understand.
A:
One day Donna saw her son use his potty on his own.