Professor Yi went to visit Mr. Gong's house. When he arrived at the door, he didn't know how many floors Mr. Gong lived in, so he asked his grandmother and a few children who had been cooling off at the door. "The teacher can't live on the second floor. " Xiaofang said: "Mr. Gong can't live on the third floor. " Xiaohong said: "Mr. Gong can't live on the fourth floor. " Xiaoyu said: "This building has only four floors. Lived in the open air. "At this time, the grandmother smiled and said to Professor Yi:" These children are really naughty, but most of them are telling the truth, only one person is telling the truth. ". Based on this, we can launch:. ['Teacher Gong lives on the first floor.', 'Teacher Gong lives on the second floor.', 'Teacher Gong lives on the third floor.', 'Teacher Gong lives on the fourth floor.']