你好：when引导从句用过去时，主句还可以用过去完成时，和主从句都用过去时怎么区别也表动作先后发生呀

Question

如题所述

Answer 1

主句用过完时( sb. had done sth. )+when从句( when sb. did sth. ):
表示主句的动作发生在从句动作之前,如:
The train had left when they arrived at the railway station .

主句用过去进行时( sb. was doing sth. )+when从句( when sb. did sth. ):
或: 主句用一过时(sb. did sth. )+when从句用过进时( when sb. was doing sth. ):
表示主从句的动作同时发生,如:
Mother was preparing supper when I got home yesterday evening .

When the students were having a meeting, the teacher came in.

Last Sunday I met Lin Hong when I was walking in the street.

注: when从句既可放主句后,也可放主句前.