Đáp án:

19. Those books should have been taken back to the library (by you).

20. Articles can't be exchanged (by us) which customers have bought during the sale.

21. This man mustn't be moved (by you); he's too ill.

Giải thích các bước giải:

· Cấu trúc chuyển từ thể chủ động sang thể bị động dạng chung: 

CĐ: S + V + O.

BĐ: S + be + PII + (cụm từ chỉ nơi chốn) + (by + O) + (cụm từ chỉ thời gian).

· Phân tích câu 19:

- CĐ:

+ S : You

+ V : should have taken

+ O : those books back to the library

- BĐ:

+ S : Those books

+ be : should have been

+ PII : taken

+ cụm từ chỉ nơi chốn : to the library

+ by + O : by you

$\Rightarrow$ Those books should have been taken to the library (by you).

· Phân tích câu 20:

- CĐ:

+ S : We

+ V : cannot exchange

+ O : articles

- BĐ:

+ S : Articles

+ be : can't be

+ PII : exchanged

+ by O : by us

$\Rightarrow$ Articles can't be exchanged (by us) which customers have bought during the sale.

· Phân tích câu 21:

- CĐ:

+ S : You

+ V : mustn't move

+ O : this man

- BĐ:

+ S : This man

+ be : mustn't be

+ PII : moved

+ by + O : by you

$\Rightarrow$ This man musn't be moved (by you); he's too ill.