1, 

+:If I were an environmentalist,i would find a way to reduce the pollutions

+:If I were an environmentalist,i would find a solution for the global warming

2,

+:If our school had a big garden,we could breathe more fresh air
+:If our school had a big garden,we would have larger area

3,

+:If you want to do something for the planet,you should find a solution for global warming
+:If you want to do something for the planet,you should make someting for it

1.If I were an environmentalist, I would creat a device cleaning the ocean

If I were an environmentalist, I will make the rule about fining people who litter

2.If our school had a big garden, I would plant some trees

If our school had a big garden, I would take care of the garden

3.If you want to do something for the planet, you shouldn't litter

If you want to do something for the planet, you should protect the forests against deforestation