43. D Nam said that they were learning English at that moment.

`->` Cấu trúc câu trần thuật: S + said + (that) + S2 + V lùi thì ( chuyển từ hiện tại tiếp diễn sang quá khứ tiếp diễn, thay "we" thành "they", "this moment" thành "that moment" )

44. B My mother is a more careful driver than my brother.

`->` Mẹ tôi là người lái xe cẩn thận hơn anh/em tôi.

45. C She used to walk to school when she was in primary school.

`->` used to + Vinf: đã từng làm việc gì trong quá khứ

46. B It is beleived that you will be pleased with your exam.

47. C A new school was built in my village last year.

`->` Câu bị động quá khứ đơn: S + was/were + Vpp + nơi chốn + by SO + thời gian 

48. A Lan didn't go to school last Friday because she was sick.

`->` because + S + V: bởi vì

49. C Vietnam, which is in the Southeast Asia, exports .........

`->` which thay cho vật trong mệnh đề quan hệ

50. A My younger sister used to cry a lot when she was a baby.

`->` used to + Vinf: đã từng làm việc gì trong quá khứ

46. C

47. C

48. A

49. B

50. A