Ms Li is talking some changes of two cities to her students on class. She asked Bob and Sue to answer these questions.

Ms Li : Now, our city is quite different. Do you know what changes of some cities?

Bob : 30 years ago, there were no bridges. Now, there are two train stations. There were some factories. Now, there are twenty shopping malls. 40 years ago, people went some places by a track or by a bike. Now, they go there by bus or in a car.

Ms Li : Very good, Bob. You are a carefully boy. Who can tell me what changes of Shenzhen's traffics?

Sue : there were some factories around us. There are many shopping malls now, just as Renrenle Mall, Walmark Mall and Suibao Mall… 20 years ago, people went out on walk or by bikes. Now, people go out in a personal （私人的） car or by train.

Ms Li : Yes, good, thank you Sue.