1. After David had gone home, we arrived 

- After + QKHT (hành động xảy ra trước), QKĐ (hành động xảy ra sau)

2. Before we took a look around the shops, we had lunch

- Chúng tôi ăn trưa rồi mới đi dạo shop -> ăn trưa trước, dạo shop sau

- Before QKĐ (hành động xảy ra sau),  QKHT (hành động xảy ra trước)

3. When we got out of the office, the light had gone down 

-  When QKĐ (hành động xảy ra sau),  QKHT (hành động xảy ra trước)

4. By the time we started our work, she had explained everything clearly

- By the time = Before 

- Before QKĐ (hành động xảy ra sau),  QKHT (hành động xảy ra trước)

5. Before my mother came home, my father had watered all the plants in the garden 

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- Vế chia QKHT luôn xảy ra trước vế chia QKĐ nên bạn có thể dựa vào đó mà biết sự việc nào xảy ra trước hay sau

`@Sky`

`-` After David had gone, we arrived.

`-` Before we took a look around the shops, we had lunch.

`-` When we got out of the office, the light had gone out. 

`-` By the time we started our work, she had explained everything clearly.

`-` Before my mother came home, my father had watered all the plants in the garden. 

`-------------------------------------------------`

Công thức thì QKHT: 

`(+)` S + had + V3/Ved

`(-)` S + had not (hadn't) + V3/ Ved

`(?)` Had + S + V3/ Ved ?

Sau "after" dùng thì QKHT, sau "before" hoặc "by the time" dùng thì QKĐ.