根据对话内容，在每小题的空白处写出一个完整的句子，使对话意思完整。 John: Oh, Tom. Please don't sit on this chair! Tom: 1. ? John: Look! One of its legs is broken. It's dangerous to sit on it. Tom: 2. . Who's broken it? John: I don't know. I found it this morning when I was cleaning the floor. Tom: Let's tell our teacher about it and then someone can repair it. John: No. 3. . Tom: Yourself? Have you learnt to repair a chair? John: Yes. My father is a worker. He is good at repairing things. 4. . Tom: Oh, your father taught you. 5. ? John: Certainly. Let's begin.