is和am的过去式和过去分词

　　We had to work within the parameters that had already been established.

　　我们必须在已设定的范围内工作。

　　No new SARS cases have been reported in the region.

　　该区没有新增非典型肺炎病例。

　　The information has been placed in the public domain.

　　这资料不受版权保护。