例句：

　　He is a bus driver. ----- He was a bus driver.

　　am的`過去式是“was ”，過去分詞是“been ”,主語為"I"；

　　例句：

　　I am a student. ---- I was a student.

　　are的過去式是“were”，過去分詞是“been ”。are是復數，主語用you， we ，they。

　　例句：

　　They are basketball players. ---- They were basketball players.