be的过去分词是 was/were。
1. was used to indicate that something was previously mentioned or done.
例句：The party was held in the last week of last month.
2. were used to indicate that something was previously mentioned or done, but not necessarily done or mentioned again.
例句：I was born in 1980, and I was in high school when the internet was first introduced.
3. was/were used as a verb in the past tense to indicate the past simple, but with a sense of emphasis on the past.
例句：We were discussing the latest fashion trends when she arrived.
4. was/were used as a verb in the past tense to indicate the past perfect.
例句：We have been to Europe twice before, and we are planning to go again next year.
5. was/were used as a verb in the past tense to indicate the past perfect continuous.
例句：He was working as a teacher at the time of the accident.
总结起来，was/were used in different ways to indicate the past, but the main use was to indicate the past simple, past perfect, past perfect continuous and past perfect passive.
