are的原形

am is are 是同一类词。称为系动词。系动词与表语(可以是名词，形容词，副词，非谓语，从句等)一起构成谓语，说明主语的职业，身份和状态。例如：He is a teacher.他是一名教师。She is short. 她个矮。The film is on. 电影在上映。I am to travel next week. 我计划下周去旅行。The city is not what it was in the past.

am， is， are 的原形动词是be。过去式和过去分词为was/were， been