21. was cooking 

When + QKĐ, QKTD

QKTD: S + was/were + Ving 

22. would disappear 

S + said +(that) + S+ V (lùi thì)

DHNB: in 30 years (TLD)

S + will  +v1 

will ⇒ would 

23. gathers

as soon as + HTĐ , TLĐ

S số ít + Vs/es: thì HTĐ

24. invented 

DHNB: in 1642 (QKD)

S  +V2/ed 

25. Nancy saw a UFO when she was reading in the garden.

QKĐ + when + QKTD

26. The teacher wanted to know why I was late for the conference.

S + wanted to know + Wh + S+ V (lùi thì)

HTD ⇒ QKD

S + be  +ADJ 

27. Where will people live in the future? 

Wh + will + S +V1? thì TLĐ

28. The school organises a science meeting on Sundays. 

S số ít + Vs/es 

a + N số ít 

on + ngày 

29. Peter said that he didn't have a good book.

S + said +(that) + S+ V (lùi thì)

HTĐ ⇒ QKĐ

30. She asked me where I went every week.

S + asked + O + WH + S+ V (lùi thì)

HTĐ ⇒ QKĐ

31. My classmate speaks English more fluently than me.

S + V+  more + long+adv + than + O : ss hơn 

32. Mr. Robert said that he would go to Cairo the next day.

S + said +(that) + S+ V (lùi thì)

will ⇒ would 

tomorrow ⇒ the next day / the following day 

`color{orange}{~MiaMB~}`