1. He asked Lan what she was doing then.

S+ asked + O + WH + S +V (lùi thì)

HTTD --> QKTD

now --> then 

2. He asked Lan what her job was.

S+ asked + O + WH + S +V (lùi thì)

HTĐ --> QKĐ

3. He said that he had never seen that place before. 

S + said (that) + S+ V (lùi thì)

HTHT --> QKHT

this --> that 

4. While my dad was typing, my mom was cooking last night.

While + QKTD, QKTD: hành động xảy ra song song / cùng lúc ở 1 thời điểm trong qk

5. When I was taking a shower, someone knocked at the door.

When + QKTD, QKĐ: hành động đang xảy ra thì có hành động cắt ngang 

6. She said that she had decided to go on holiday in Singapore. 

S + said (that) + S+ V (lùi thì)

HTHT --> QKHT

7. They said that they were playing chess then.

S + said (that) + S+ V (lùi thì)

HTTD --> QKTD

now --> then 

`color{orange}{~MiaMB~}`