在英语中，动词的变位非常重要，它可以表示不同的人称、时态和语气。而be动词是英语中最常用的动词之一，形式上有一般现在时(am/is/are)、一般过去时(was/were)、现在分词(am/is/are being)和过去分词(been)四种。今天，我们就来了解一下be动词的过去式。
1. am 的过去式是 was，is 的过去式是 was，are 的过去式是 were，这三个都是不规则动词，因此需要特殊记忆。例如，I am a teacher. 和 He is a doctor. 转换成过去式应该分别是 I was a teacher. 和 He was a doctor. 而 They are students. 的过去式应该是 They were students.
2. be 动词的过去式也可以用于描述一件过去的状态，例如 I was happy yesterday.、She was tired after work 等。这里的 was 和 were 均属于 be 动词的过去式。
3. be 动词还可以与过去分词搭配，构成被动语态。例如 The book was written by him. 和 The song was sung by her. 这里的 was 和 were 也是 be 动词的过去式。如果要将被动语态转换成主动语态，则需要注意句子的人称和时态，并采用相应的动词形式。
