听力原文： Toronto is one of the largest cities in Canada. It is located in the province of Ontario. A special feature of Toronto is the downtown area—covering about twelve square kilometers—where many shops and buildings are located underground. There are five major shopping centers and a convention center with hotels. A subway and underground passageways connect these buildings with each other and the streets above. The architectural design is appropriate and popular because of the weather conditions in Toronto. The temperature fluctuates widely from summer to winter—by as much as 40 degrees Celsius within a year. This underground area has also helped to keep business in the city center instead of moving out to the suburbs, which is happening in many other cities. We think that makes Toronto a special place. What is the talk mainly about?