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Our world is facing many problems. One of the biggest is the ①（ ） population. Every year, more babies are born and people also live ②（ ）. The growing population means the growing need for ③（ ）, food and clean water. People also need better bus and train services. The large population brings another huge ④（ ） for the world: pollution. People also produce ⑤（ ） rubbish. In many areas, the rivers are seriously polluted and people have to walk a long way ⑥（ ） clean water. We must work harder to protect our world against pollution.
