- Had you been waiting long before the taxi arrived?
- We had been trying to open the door for five minutes when Jane found her key.
- It had been raining hard for several hours and the streets were very wet.
- Her friends had been thinking of calling the police when she walked in.
- Jane said, "I have been gardening all afternoon." = Jane said she had been gardening all afternoon.
- When the police questioned him, John said, "I was working late in the office that night." = When the police questioned him, John told them he had been working late in the office that night.
过去完成进行时是由两个要素构成——Be 动词的过去完成时 (=had been) + 现在分词（动词原型+ing）。
过去完成进行时，以 to buy 为例
|I had been buying||I hadn't been buying||Had I been buying?|
|You had been buying||You hadn't been buying||Had you been buying?|
|She had been buying||She hadn't been buying||Had she been buying?|
|We had been buying||We hadn't been buying||Had we been buying?|
|They had been buying||They hadn't been buying||Had they been buying?|