改成过去式,肯定是要改句子中的动词
e.g 一般说 He has breakfast at 7 o'clock.
如果两人对话,想表达“他已经吃过饭了,7点钟吃的”那就要写成“He had breakfast at 7 o'clock”
一般的句子都可以改成过去式,但通常是有语境的,都是表达已经发生过的事情.
She went home just now.她刚才回家了
He finished the class last year.他去年就完成了课程
She became a teacher 2 years ago.两年前她做了老师