Rivers are one of our most important natural resources. A n{#blank#}1{#/blank#} of the world's great cities are located on rivers, and almost each country has at least one river f{#blank#}2{#/blank#} through it that p{#blank#}3{#/blank#} an important part in the lives of its people.

    Since the beginning of history, people have been using rivers for transportation. The longest one in the United States is the Mississippi, and the lifeline of Egypt is the Nile. A{#blank#}4{#/blank#} from transportation, rivers give water to drink, water for crops, and chances for fun and recreation for the people who live along their banks.

    However, large cities and industries that are located on rivers often make problems. As the cities grow in size and industries increase in number, the water in the rivers becomes p{#blank#}5{#/blank#} with chemicals and other harmful materials.

    Experts a{#blank#}6{#/blank#}that environmental organizations should work together with different communities and countries to find solutions to the serious environmental problem. As c{#blank#}7{#/blank#} of the Earth, we all have a responsibility to preserve and sustain the environment we have-for ourselves and our future generations. After all, there is no s{#blank#}8{#/blank#} for our Earth. It's all we've got to live on.