1.Your English doesn’t improve because you don’t practice it regularly.
If. . .you don't practice english regularly, it won't improve . . . . . . . . 
2.The last time I saw David was in 1990.
I haven’t . . . . seen david since 1990. . . . . . . . . . . . . . . . . . .
3.If I didn’t have a key, I couldn’t get into the room
Unless. . . . .i had a key, i couldn't get into the room  . . . . .  (unless= if not)
4.Nam doesn’t buy a new car because he doesn’t have enough money.
If. . . . . nam had enough money, he could buy a new car. . . . . . . . . . . . . . . . . . . . . . . . . . .
5. I said to my friends “turn off all the lights when you go out”
I asked. . . . .my friends to turn off all the lights when they went out. . . . . . . . . . . . . . . . . . . .
6. Ba is not intelligent. He can not do these exercises.
Ba is too. . . . . . . . .unintelligent to do the exercises  . . . . . . . . . . . . .
7. She is too young to decide herself.
She isn’t. . . . . old enough to decide herself. . . . . . . . . . . . . . . . . . . . . . . . . . 
8.The last time she had a swim was three years ago.
She hahasn’t. . . swam for 3 years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9. “ What do you usually do in your free time?”
The examiner asked me. . . what i usually did in my free time . . . . . . . . . . . . . . . . . . . . . 
10. They are painting the living room at the moment.
The living room. . . . is being painted at the moment . . . . . . . . . . . . . . . . . . . 
11. “ Don’t go out tonight because it is very dangerous” She asked me.
She asked me. . not to go out that night because it was very dangerous . . . . . . . . . . . . . 
12. The bread is so stale that we can’t eat it.
The bread isn’t. . fresh enough for us to eat . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
13. If it don’t stop raining, we won’t get home.
Unless . . . .it stops raining, we won't get home . . . . . . . . . . . . . . . . . . . . . . . . . 
14. I have never read such a romantic story.
This is . . . . the first time i've ever read a romantic story . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15. “ Is your father working in the garden with your friends now, Nam”?
He asked. . . . . . .nam if his father was working in the gardent with his friends then . . . . . . . . . . 
16. In spite of his age, he often plays badminton.
Although. . . . . . .he is old, he often plays badminton  . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17. The bicycle was so expensive that I didn’t buy it.
The bicycle was too. . . . . . expensive for me to buy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18. He asked Jane how she thought of his new clothes.
He asked Jane “ How. . . . . .do you think of my new clothes . . . . . . . . . . . . . . . . . . . . . .
19. My uncle spent five hours reparing his house.
It took. . . . . my uncle 5 hours to repair his house . . . . . . . . . . . . . . . . . . . . . . . . . . . 
20. Although he lives far away from the office , he cycles to work.
Despite. . . . . . . . . . . living far away from the office, he cycles to work . . . . . . . . . . . . . . .

Giải thích các bước giải :

1 . If you don't practice english regularly , your english won't improve

2 . I haven't seen David since 1990

3 . Unless I had a key , I couldn't get into the room

4 . If Nam had enough money , he could buy a new car

5 . I asked my friends to turn off all the lights when they went out

6 . Ba is too unintelligent/stupid to do the exercises

7 . She isn't old enough to decide herself

8 . She hasn’t swam for 3 years
9. 
The examiner asked me what I usually did in my free time 
10.
The living room is being painted at the moment 
11.
She asked me not to go out that night because it was very dangerous 
12. 
The bread isn’t fresh enough for us to eat 
13. 
Unless it stops raining, we won't get home 
14.
This is the first time I've ever read a romantic story
15. 
He asked Nam if his father was working in the gardent with his friends then 

16
Although he is old, he often plays badminton 
17. 
The bicycle was too expensive for me to buy

18 . 
He asked Jane “ How do you think of my new clothes 
19. 
It took my uncle 5 hours to repair his house
20. 
Despite living far away from the office, he cycles to work