A boy and his father visiting from a third world country were at Lakeside Mall. They were amazed by almost everything they saw，but especially by two shiny，silver walls that could move apart and back together again. The boy asked his father，“What is this，Father？”The father responded，“Son，I have never seen anything like this in my life. I don’t know what it is！” While the boy and his father were watching widely-eyed，an old lady in a wheel chair rolled up to the moving walls and pressed a button...