主语+be+过去分词+by+人物.
be词根据句子不同时态而变化.
(1)The letter is written by him.
(2)The floor was swept by her.
(3)This hospital was set up in 1975.
(4)He was saved at last.
(5)The work has been done.
(6) The railway was being built this time last year.
(7) A new railway is being built in this city.
(8) He told us that the new railway would be built the next year.
(9)Knives are used for cutting things.
一般现在时：am／is／are＋V-ed
一般过去时：was／were＋V-ed
一般将来时：will／shall be＋V-ed
现在进行时：am／is／are being＋V-ed
过去进行时：was / were being + V-ed
现在完成时：have／has been＋V-ed
过去完成时：had been＋V-ed
将来完成时：shall / will have been + V-ed
过去将来完成时：would / should have been + V-ed