I.

37. must/ mustn't + V nguyên thể → bỏ "to"

38. children là danh từ số nhiều

→ thay has thành have

39. when I came → quá khứ

→ thay is having thành was having

40. không mua được vì ....

→ chuyển while thành because

41. Chủ ngữ là "you"

→ thay has thành have

42. disrespectful: không tôn trọng → không nên như vậy

→ chuyển should thành shouldn't

43. sau to dùng V nguyên thể

→ chuyển has thành have

44. sau should dùng V nguyên thể

→ bỏ "to" đi

45. have avoid → have to avoid

II.

1. Lang Lieu couldn't buy any special food because he was very poor.

2. During Tet, Vietnamese people buy all kinds of sweets so they make Chung cakes as well.

3. The Hung King Temple Festival was a local festival; however, it has become a public holiday in Viet Nam since 2007.

4. At the Mid-Autumn Festival, kids can sing, dance, and enjoy mooncakes; therefore, every child likes it very much.

5. We don't celebrate the festival if it costs too much money.

37. must

38. children 

→ thay has thành have

39. when I came → quá khứ

→ thay is having thành was having

40. không mua được vì ....

→ chuyển while thành because

41. Chủ ngữ là "you"

→ thay has thành have

42. disrespectful: không tôn trọng → không nên như vậy

→ chuyển should thành shouldn't

43. sau to dùng V nguyên thể

→ chuyển has thành have

44. sau should dùng V nguyên thể

→ bỏ "to" đi

45. have avoid → have to avoid

II.

1. Lang Lieu couldn't buy any special food because he was very poor.

2. During Tet, Vietnamese people buy all kinds of sweets so they make Chung cakes as well.

3. The Hung King Temple Festival was a local festival; however, it has become a public holiday in Viet Nam since 2007.

4. At the Mid-Autumn Festival, kids can sing, dance, and enjoy mooncakes; therefore, every child likes it very much.

5. We don't celebrate the festival if it costs too much money.