41. Mary and John said that they didn't know those two girls very well.

S + said + (that) + S + V (lùi thì)

HTĐ ⇒ QKĐ

these ⇒ those 

42. A new school will be sold this year.

S + will be + V3/ed: bị động - TLĐ

43. They haven't talked to each other for two weeks.

S + has/have+ not +V3/ed+ for/since + time 

44. The more books you read, the more knowledge you will have.

The more + N + S + V, the more + N + S + V : càng  ... càng

45. I spent half an hour writing that letter.

S + spent+ time + Ving: ai dành bao nhiêu thời gian làm gì 

46. She couldn't come to class because of her illness.

Clause + because of + N /NP / Ving: bởi vì 

47. She dances ballet very excellently.

S+  V+ ADV

48. It's too cold for us to go swimming today.

S +be+ too + ADJ + (for O) + to V: quá ... đến nỗi không 

49. If he weren't ill he could participate in the match.

If 2: if + S + were, S + would / could +V1 

50. This is the first time I have been to Hoi An.

This/ It is the first time + S+ has/have+ V3/ed 

`color{orange}{~MiaMB~}`