have过去式 had；过去分词 had；has是have的第三人称单数。
has有有过去式和过去分词。
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。
I think you have made an error in calculating the total.
我想你在计算总数时出了差错。
No new SARS cases have been reported in the region.
该区没有新增非典型肺炎病例。
