has been是什么时态？

　　例句：

　　Only time will tell if the treatment has been successful.

　　只有时间才能证明这种疗法是否成功。

　　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。