city前面用a还是the

city的前面用a和the都可以

例句

1、

A new system has been devised to control traffic in the city.

控制城市交通的新系统已经设计出来。

2、

The city is a mixture of old and new buildings.

这座城市是新老建筑兼而有之。

3、

The book aims to cover all aspects of city life.

这本书旨在涵盖城市生活的各个方面。