after which,

一、句子分析：
主语：the factory
并列谓语 1：was bombed twice by Nato 被北大西洋公约组织的轰炸了两次
—— was bombed 是被动语态,twice 是副词,说明 bombed 的频度.
并列谓语 2：and sustained heavy damage 遭受到严重的破坏
—— 主动语态,等于 the factory sustained heavy damag
定语从句：after which production ceased 轰炸以后生产停止
—— which 指代 heavy damage ,如果变成独立的句子就等于 production ceased after the heavy damage
二、关于“介词 + 关系代词”
定语从句中,如果指代先行词的关系代词是从句中的介词宾语,那么 which 可以与介词一起提前放在从句的首位,如：
This is the house in which he has lived for some years.这就是那间他住了几年的房子.
——等于介词后置的 This is the house which he has lived for some years in,改写为两个独立的句子为：
* This is the house.
* He has lived in the house for some years.
We began to use the tool of which we once took the place 我们开始使用了曾经替代过的那种工具.
—— 等于 We began to use the tool which we once took the place of ,可改写为：
* We began to use the tool.
* We once took the place of the tool.