2015-2016学年 北师大版 必修三 Unit9 Wheels lesson1课件 (7)
2015-2016学年 北师大版 必修三  Unit9 Wheels lesson1课件 (7)第2页

 People are on move. The means of transportation are more and more important. With the development of science and technology, transportation in cities is improving, but with the convenience it has brought to us, some other problems are coming out. …