用法：在過去的時(shí)間里，兩個(gè)動(dòng)作中，發(fā)生在前的那個(gè)動(dòng)作要用過去完成時(shí)。
結(jié)構(gòu)：had+過去分詞
After she had finished her homework, she went shopping.
They had sold the car before I asked the price.
The train had left before I arrived at the station.
After/before引導(dǎo)的時(shí)間狀語從句放在句首要在句子后面加逗號(hào)，如果放在主句后則不用加。
1.變疑問句將助動(dòng)詞移到句首
Had she finished her homework?
2. 變否定句在助動(dòng)詞后面加not
She hadn’t finished her homework.
3. 肯定回答及否定回答
Yes, she had. No, she hadn’t.
4.特殊疑問句：
What had she done?