`1`. After David had gone home, we arrived.

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

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

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

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

* Cấu trúc: 

By the time + quá khứ đơn, quá khứ hoàn thành

When + quá khứ đơn, quá khứ hoàn thành

Before + quá khứ đơn, quá khứ hoàn thành

After + quá khứ hoàn thành, quá khứ đơn 

Qúa khứ hoàn thành dùng cho hành động xảy ra trước ( S + had + Vpp )

Qúa khứ đơn dùng cho hành động xảy ra sau ( S + V2/ed )

1-After we arrived, Davied had gone home.

CT của after:  After simple past, + simple past

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

CT của before: Before + simple past, + past perfect

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

CT của when: When + past continuous (clear point of time - thời gian cụ thể), + simple past

4-By the time we started our worked, she had explained everything dearly.

CT của by the time: By the time + S1 + V1(ed/PI), S2 + had + V(ed/PII)

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