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1 more than 7 billion
2 the population is doubling every forty years.
3 Because doctors learnt more about what made people sick.And they leant how to make people well again,so people began to live long lives.
4 Because there were no hospitals and no doctors.
5 The water in our rivers will become too dirty to drink.The air will become dirtier too.We will destory ourselves and our beautiful world.