`1`. Our teacher said that they were learning more about universe.

- Câu tường thuật với câu trần thuật: S + said + (that) + S + V (lùi thì)

- we -> they ; Hiện tại tiếp diễn -> Quá khứ tiếp diễn

`2`. Dr. Nelson said that scientists had made various applications in long distance communication.

- Hiện tại hoàn thành -> Quá khứ hoàn thành

`3`. Our Chemistry teacher told us that science was a good and useful servant but it was a bad destructive master.

- Hiện tại đơn -> Quá khứ đơn

- Câu tường thuật với câu trần thuật: S + said to/told + O + (that) + S + V (lùi thì)

`4`. Our headmaster told us that space tourism would broaden our knowledge of space.

- will -> would

`5`. Our Math teacher said that professor Le Van Thiem had believed in the importance of education and science, so he had founded a teacher training college and a college of fundamental science.

- Quá khứ đơn -> Quá khứ hoàn thành

`1.`Our teacher said that they were learning more about universe.

`2.`Dr. Nelson said that scientists had made various applications in long distance communication.

`3.`Our Chemistry teacher told us that science was a good and useful servant but it was a bad destructive master.

`4.` Our headmaster told us that space tourism would broaden our knowledge of space.

`5.`Our Math teacher said that professor Le Van Thiem had believed in the importance of education and science, so he had founded a teacher training college and a college of fundamental science.

`@` Kiến thức câu gián tiếp :

`+` S + said + (that) + S + V (đổi ngôi/lùi thì)

`+` Quá khứ đơn `->` Quá khứ hoàn thành

`+`Hiện tại tiếp diễn `->` Quá khứ tiếp diễn

`+`Hiện tại đơn `->` Quá khứ đơn

`+` will `->` would