46. My sister took care of our children when we were away.

47. Minh hasn't written to his pen pal for five months.

48. It took my father years to build up his collection.

49. A new kind of plant has just been produced (by them).

50. I wish our teacher were here at the moment.

51. Your father watched a football match on TV last night, didn't he?

52. Even though Mai is very sleepy, she tries to finish her homework.

53. If you don't study hard, you will fail in the next exams.

54. C1 : Would you mind lending me your smart phone?

      C2 : Would you mind if I borrowed your smart phone?

55. He asked his friend if it would rain the following morning.

Chúc bạn học tốt !!!

46. My sister looked after our children when we were away.
 -My sister took care of our children when we were away
47. Minh last wrote to his pen pal five months ago
. - Minh hasn't written to his pen pal for 5 months
48. My father spent years building up his collection. 
- It takes my father years to build up his collection
49. They have just produced a new kind of plant.
 A new kind of plant has just been produced
50. What a pity! Our teacher isn't here at the moment. 
- I wish our teacher were here at the moment
 51. Did your father watch a football match on TV last night? 
- Your father watched a football match on TV last night, didn't he
 52. Mai is very sleepy. She tries to finish her homework. 
Even though. Mai is very sleepy, she tries to finish her homework
 53. Study hard or you will fail in the next exams. 
If .you don't study hard, you will fail in the next exams
54. May I borrow your smartphone? 
Would you mind lending me your smartphone
55. "Will it rain tomorrow morning?", he asked his friend
. - He asked his friend...if it would rain tomorrow the day after