`\color{#145277}{N}\color{#246483}{a}\color{#34768F} {e}\color{#44889B}{u}\color{#539AA7}{n}`

1. He had a very happy childhood.

- time as a child = childhood (n): tuổi thơ

- Thì QKĐ : S + V2/ed

2. His achievements impressed people.

- Bị động QKĐ : S + was / were + V3 / ed

3. While visiting Japan, my father bought a lot of souvenirs.

- While + V-ing, QKĐ : Trong khi (Dùng khi `2` hành động xảy ra song song)

4. When he arrived at work, a meeting was occurring.

- When + QKĐ, QKTD : Khi (Dùng khi `1` hành động đang xảy ra thì có `1` hành động khác xen vào)