Instructions: The task is about reading the given story and question, then finding an answer to the given question. Based on the passage provided and the given question, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Input: story: Art lovers around the world have thought about this question for so many years: what is the secret behind the Mona Lisa's smile? However, they can ask Mona Lisa herself in the interactive exhibition in Beijing. This exhibition brings the 500-year-old painting to life. Now Leonardo da Vinci's famous painting can move her head and wave her hand in 3D, and even answer questions. She can answer the questions about her life, her age and so on. But when she talks she doesn't speak Italian but Chinese like: "Da jia hao, wo jiao Mengna Lisha. Hen gao xing jian dao ni men." The new, digital picture of Mona Lisa is the center piece of the World Classic Interactive Arts Exhibition in Beijing. You can also see other world-famous paintings such as Leonardo da Vinci's Last Supper. Last Supper is another picture that they made alive with 3D. In this picture, Jesus can walk and talk with his believers . It took the organizer Wang Hui and over 400 digital artists in South Korea two years to make the picture, at a cost of around 50 million yuan. He says, "What's special about it is that it's the first time to use computer technology to make her speak and move." So what does the Mona Lisa say if you ask her why she is smiling?, question: What do people wonder about?
Output:
the secret behind the Mona Lisa's smile