3. The teacher doesn't correct exercises.
$\longrightarrow$ Exercises are not done correct by the teacher.
4. How many trees do they cut down to build that fence?
$\longrightarrow$ How many trees are cut down to build that fence?
5. This well-known library attracts many people.
$\longrightarrow$ Many people are attracted by this well-known library
6. All students attend the meeting.
$\longrightarrow$ the meeting is attended by all students
7. He repairs my bike.
$\longrightarrow$ My bike is repaired by him.
8. Mr. Smith teaches us French.
$\longrightarrow$ Our French is taught by Mr.Smith.
9. They don't look after the children properly.
$\longrightarrow$ The children are not looked after properly by them.
10. Nobody sweep this street.
$\longrightarrow$ This street is not sweeped.
11. People drink a great deal of tea in England.
$\longrightarrow$ A great deal of tea is drunk in England.
12. People speak English all over the world.
$\longrightarrow$ English is spoken all over the world.