be 有3个形式： is , am, are.
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一个使用口诀是： 我用am. 你用are. is 跟着他,她,它.
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总之,
现在时：I am ,You are , He / She / It is .
过去时：I / She / He was. You / They were.
be 动词+动词（不定式,动名词ing, 分词）.
例子： I am good. He is good.You are good.
I was doing my homework.
They were to go swimming when I saw them.
The book was given by my sister.