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if we (throw away) less rubbish our planet would be cleaner/

if i...(be) you, i would join greenpeace

if you had  read these books you (know) more about enviromental problems.

if people (avoid) damaging nature many species of animals wouldnt have disappeared

 

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If we threw away less rubbish our planet would be cleaner.

If I were you, I would join Greenpeace.

If you had read these books, you would have known more about environmental problems.

If people had avoid damaging nature, many species of animals wouldn't have disappeared.