The system has been in operation for six months.

　　這個系統已經運行六個月了。

　　The company has been investing in new plant and equipment.

　　這家公司一直在投資購置新機器和設備。

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

　　控制城市交通的'新系統已經設計出來。

　　Digital television has been around for some time now.

　　數字電視已經面市一段時間了。

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

　　在控制瘧疾方面已取得新的進展。