1, Huong doesn't tidy the house.Her mum feels angry 

If huong tidied the house, her mum wouldn't feel angry

2 the air is polluted . people get can diseases

the more polluted the air is, the more diseases people can get

3 the polluted water makes a lot of underwater creatures die 

 a lot of underwater creatures die due to the polluted water

4 it is necessary for us to use water carefully 

we need to use water carefully

5 air pollution has reduced dramatically over the last few years

there has been a dramatic reduction in air pollution over the last few years