21.B chuyển thành reading là đúng vì enjoy + ving

22.B chuyển thành  who sings là đúng vì Mr thanh là số ít

23.B chuyển thành not to spend là đúng vì to + v1

24.C ko cần more nữa

25.B  chuyển thành natural resouces vì  ở đây ta cần natural

26.C

27.B

28.A

29.B

30.A

31.That old house has been sold by them.

32.Although the weather was bad, they had a wonderful holiday.

33.A new mail will be built here by them.

34.If he doesn't take these pills,he will not be beter.

35.Although he works hard,he can not support his large family.

36.If it doesn't rain tomorrow I will go camping my  with my friends

37.If I met ailen from outer space I would invite their home and talk.

38.I have never travelled by air.

39.. The students are studying for their exam now.

40.It was such a cold day that we decided not to go out.

II: 20, D

III: 21, B→reading

22, B→who sings

23, B→not to spend

24, C→than

25, B→natural resources

IV: 26, C

27, B

28, A

29, B

30, A

V: 31, That old house has just been sold

32, Although the weather was bad, they had a wonderful holiday

33, A new more will be built here

34, If he doesn't take this pills, he won't be better

35, Althought he works hard, he can't support his large family

VI: 36, If it doesn't rain tomorrow, I will go camping with my friends

37, If I met the ailen from outer space, I would invite it to go home and talk

38, I have never travelled by air

39, The students are studying for the exam now

40, It was such a cold day that we decided not to go out

41, If I were you, I would learn harder