情绪形容词：happy, sad, angry, tired等 — 英语阅读题

Read and answer. 阅读短文，回答问题。 It is Friday afternoon. Lily, Tom and Sam are at school after class. Lily gets a new storybook from her friend. She jumps and smiles. She is very happy. Tom can not find his toy dog. He looks for it everywhere, but it is not there. He feels sad. Sam runs a long way to school this morning. Now he sits on the chair and wants to sleep. He is very tired. Miss Li sees Lily's toy dog on the desk. It is Tom's dog! She gives it to Tom. Now Tom is not sad. He smiles too. He is happy again. Question: Why is Tom happy at the end of the story? 从文中找出原因，用简短英语或中文作答。