_`text{KathrynHan}`

`=>` By the time we arrived at the airport, the plane had taken off.

`-` QKĐ + before (trước) + QKĐ

`->` By the time (Vào lúc) + QKĐ, QKHT

`-` Thì QKĐ: S + V-ed/III

`-` Thì QKHT: S + had + V-III

`-` take(:) off: cất cánh

Dịch: Khi chúng tôi tới sân bay thì máy bay đã cất cánh.