They have been expanding, urbanization has been expanding, at an exponential rate in the last 200 years so that by the second part of this century, the planet will be completely dominated by cities.
它们一直在扩张 城市化的扩张速度 在过去的200年里变得越来越快 到了本世纪下半叶 整个地球都将被城市 所主宰