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引導的時間狀語從句放在句首要在句子后面加逗號，如果放在主句后則不用加。★ 變疑問句將助動詞移到句首
Had she finished her homework?★ 變否定句在助動詞后面加not
She hadn't finished her homework.★ 肯定回答及否定回答
Yes, she had. / No, she hadn't.★ 特殊疑問句
What had she done?