1.Students are more aware of protecting the environment. Teachers teach environmental issues at school.

If teachers didn't taught environmental issues at school , students wouldn't be more aware of protecting the environment

2.People speak English all over the world.

=>English is spoken  all over the world.

3.Many rivers and lakes are poisoned.Factories produce waste and pour it into rivers and lakes.

Because  factories produce waste and pour it into rivers and lakes, many rivers and lakes are poisoned.

4.They provided food then cleared up the debris.

=>After they had provided food  , they  cleared up the debris.
5. Vietnamese students are obligated to wear uniforms when they go to school. (HAVE)
Vietnamese students have to wear uniforms when they go to school.

6. You are not allowed to use your mobile phone on the plane. (MUSTN’T)
You musn't use your mobile phone on the plane.

7. People recycle old car tires to make shoes and sandals.

Old car tires are recycled  to make shoes and sandals.