has been 过去分词是什么时态

The system has been in operation for six months.

这个系统已经运行六个月了。

The company has been investing in new plant and equipment.

这家公司一直在投资购置新机器和设备。

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。

Digital television has been around for some time now.

数字电视已经面市一段时间了。

A new advance has been made in the control of malaria.

在控制疟疾方面已取得新的进展。