单项选择题

Large modem cities are too big to control. They impose their own living conditions on the people who live in them. Citizens are obliged by their surroundings to take a wholly unnatural way of life. They lose touch with the land and rhythm (节奏) of nature. It is possible to live in such air-conditioned (装有空调的) houses in a large city that you can hardly know the seasons. A few flowers in a public park (if you have the time to visit it) may make you remember that it is spring or summer. A few leaves on the sidewalk may cause you to remember that it is autumn. Beyond that, what is going on in nature seems to have nothing to do with you. All the simple, good things of life like sunshine and fresh air are hard to get. Tall buildings shut out the sun. Waste gases from cars, buses and trucks pollute the atmosphere.
Even the difference between day and night is lost. The flow of cars, buses and trucks goes on constantly and noise never stops.
Which of the following statement is NOT mentioned in the passage