The most touching book in the world

Wandering aimlessly on the street, I was attracted by the sweet smell of the cold wind. It was roasted sweet potatoes, steaming hot, fragrant and sweet. I smelled the fragrance and walked to the stall by the street. The person who was selling roasted sweet potatoes was physically disabled and looked very tired in the cold wind. I decided to buy more sweet potatoes and help him in the way I thought was appropriate. However, I looked at him and felt a little regretful. I really felt sorry for troubling such a disabled person to roast sweet potatoes. It seemed that he was living on a tight budget. At this moment, a boy ran over from afar and said," Auntie, my father is not feeling well. Please wait a moment. I'll roast sweet potatoes for you." After saying that, he put down his bag and started to get busy. Judging from his quick and skilled movements, he often came to help his father after school. What a filial child. I suddenly had the idea of picking out some good books to give to this child. "You still have to help Dad out late every day after school. Are you tired?" I asked. The boy denied with a smile. "Do you need any books for school? Auntie runs many chain bookstores. Go and pick some." After saying that, I felt a little regretful. This child must be very strong. He might not accept help with sympathy. As expected, I was politely rejected. However, the boy said proudly to me,"Auntie, I can read the best book in the world every day!" "Is that so? What book is worthy of your praise?" "To me, the best book in the world is the words 'Four Roasted Sweet Potato for 2,000 Korean won' written by my father! For the sake of the whole family, no matter how inconvenient his body was, he insisted on coming out to roast sweet potatoes! Every day when I see these words, I feel that my entire body is filled with endless strength. I want to work as hard as Daddy." Next to the stove, I saw the words " 2,000 won for 4 roasted sweet potatoes " written in crooked handwriting. In these crooked words, I saw the love and responsibility of a strong father for his family, as well as the worship and admiration in the children's hearts. My throat was so tight that I couldn't speak. I could only smile and nod to express my feelings to the father and son. I had so many books, but standing next to the hot sweet potato oven, I suddenly realized that it had been a long time since I had flipped through the best book in the world. Q:1. What is the "best book in the world" mentioned by the author in the article? 2." I suddenly realized that I haven't read the best book in the world for a long time." What did he mean? 3. When I saw the words " 2,000 won for four roasted sweet potatoes," why did my throat feel so tight that I couldn't speak? Please answer quickly, thank you!