Question

帮我看看这两句话对吗 英语？

（a） When I arrived at the bus station，number 20 bus was left
（b） What did you say when you from A to B?

Answer 1

（a）When I arrived at the bus station，Number 20 bus was left.句子错误，leave离开的动作发生在arrived之前已完成，表示过去的过去，要用过去完成时，had+过去分词，应改为was left改为had left。
（b）What did you say when you from A to B?when引导的时间状语从句缺乏谓语动词leave，此处say与leave是同时发生，由did，可以要用一般过去时，leave的过去式left。

Answer 2

A没有语法错误，但第二个句子用过去完成时更好。可以这样说：
When I arrived at the bus station，No.20 bus had left.
I no sooner arrived at the bus station than No.20 bus was gone.
B有语法错误，when后面的句子缺少动词，when在这里引导句子，

需要完整的主谓宾，加一个were就行了：
What did you say when you were from A to B?

Answer 3

这两句话都是病句。
第一句中的 was left 改成 had left.
第二句when 引导的从句缺少谓语动词,
from A to B 是介词短语，可以看作表语，可以添加系动词 are。

Answer 4

在我到达公交车站前、公交车已经离开了 When I arrived at the bus station, the bus had already left 在我到达公交车站前、公交车已经离开了 When I arrived at the bus station, the bus had already left

Answer 5

都不对。主要原因可能是单词的词性没有搞清楚。
第一句的“was left” 是一种系动词+表语的结构，动词不能做表语。
可以改成：When I arrived at the bus station，number 20 bus was not there。
第二句的“you from A to B”句子缺少谓语动词。

可以改成：What did you say when you was from A to B?
或者把它变成一个词语：What did you say during from A to B?