1.  After having done his homework, he went to bed. 
2.  The joke made Nam laugh a lot.
3.  Why don’t we go abroad for our holiday this year?
4.  My students study very well in Mathematics.
5.  No building is more modern than this one in this area.
6.  Because of her sickness, Lan didn’t go to school last Monday.
7.  I used to have a cat.
8.  We have been living here for fifteen years.
9.  Minh has been collecting stamps since 2000.
10.  Hoa is a hard-working student.

1. He did his homework, then he went to bed. → After having done his homework, he went to bed.

2. Nam laughed a lot when I told him the joke. → The joke made Nam laugh a lot.

3. Let's go abroad for our holiday this year. → Why don't we go abroad for our holiday this year?

4. My students are very good at Mathematics. → My students study Mathematics very well.

5. This is the most modern building in this area. → No building in this area is as modern as this one.

6. Lan didn't go to the school last Monday because she was sick. → Because of her sickness, Lan didn't go to school last Monday.

7. I had a cat once, but I don't any more. → I used to have a cat.

8. We started living here fifteen years ago. → We have been living here for fifteen years.

9. Minh began to collect stamps in 2000 → Minh has been collecting stamps since 2000.

10. Hoa is a hard student. → Hoa studies hard.