语法总结
used to 表示过去习惯
used to work / used to make 表示过去经常做而现在不再如此。
相似句：
- He used to live here.
- I used to walk to school.
which 引导定语从句
a large factory which employed... 中 which 指 factory，在从句中作主语。
相似句：
- This is the book which helped me.
- They built a house which faces the sea.