On a sunny afternoon, Ning Xiaoxi drank Coca-Cola leisurely and walked slowly to the door of the classroom. She frowned for a moment, but it disappeared in an instant. When she opened the door, it was as noisy as ever. Xiaoxi walked to her seat and sat down. Li Ya, her deskmate and friend, came up to her with a mysterious smile and said, "A handsome guy just came to see you and left a letter." After saying that, he glanced at the side of the desk. Sure enough, a small corner of a light blue envelope restlessly exposed under the book...