肯定句：主语＋be动词（was，were）＋其他；否定句：在动词后面加上not；疑问句: Be动词(Was/Were)＋主语＋其他。
(1)肯定句: 主语＋be动词(was，were)＋其他
---She was a student two years ago.两年前她是一个学生.
否定句: 主语＋be not(was not, were not)＋其他
---She was not a student two years ago.两年前她不是一个学生.
疑问句: Be动词(Was/Were)＋主语＋其他
---Was she a student two years ago?两年前她是一个学生吗?
(2)肯定句: 主语＋动词的过去式＋其他
---She ate three apples yesterday.昨天她吃了三个苹果.
否定句: 主语＋did not＋动词原型＋其他
---She did not eat three apples yesterday.昨天她没吃三个苹果.
疑问句: Did＋主语＋动词原型＋其他
---Did she eat three apples yesterday?昨天她吃了三个苹果吗?
注意:wasn't 是 was not 的缩写.weren't 是 were not 的缩写.didn't 是did not 的缩写.
含有过去式的结构句式很多，例如：I went to school by bus.
