Zhengjiang is Jack's hometown.In Jack's childhood,Zhengjiang was a city with fresh air,luxuriant trees and beautiful surroundings.But at that time,the traffice was very difficult.Bicycle and walking were the only choices of the people in the past.With the development of economy and society,there are more and more high rise buildings.The traffice has been improved drastically.But the speedy development aslo brought a lot of pollution to this city.Jack still likes the old city.Because health is the most important,living in a place without pullution is a dream of the contemporary people.