Đáp án:

`21,` Quan said his mother hadn't gone to work the previous week / the week before.

- Câu tường thuật `:` S + said ( that ) + S + V ( lùi thì )

- Lùi thì `:` QKĐ `->` QKHT $(-)$ S + hadn't + V3 / PII

- Lùi chủ ngữ `:` My `->` His

- Lùi thời gian `:` Last week `->` The previous week / the week before

`22,` Lind told me she was doing her homework then.

- Câu tường thuật `:` S + said to / told O ( that ) + S + V ( lùi thì )

- Lùi thì `:` HTTD `->` QKTD $(+)$ S + was / were + Ving

- Lùi chủ ngữ `:` I `->` She`,`my `->` her

- Lùi thời gian `:` Now `->` then

`23,` She said to me he would be there the following day / the next day.

- Câu tường thuật `:` S + said to / told O ( that ) + S + V ( lùi thì )

- Lùi thì `:` TLĐ `->` TLQK $(+)$ S + would + V

- Lùi thời gian `:` Tomorrow `->` The following day / the next day

- Lùi địa điểm `:` Here `->` There