阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将答案填写在答题卡标号为31－40的相应位置上。
Rivers are one of our most important natural resources. Many of the world’s great 【小题1】 are located on rivers, and almost 【小题2】 country has at least one river flowing through it that plays 【小题3】 important part in the lives of its people.
Since the beginning of history, people 【小题4】 (use) rivers for transportation. The longest one in the United States is the Mississippi, and the lifeline of Egypt is the Nile. 【小题5】 transportation, rivers give water to drink, water for crops, and chances for fun and recreation for the people 【小题6】 live along their banks.
However, large cities and industries that are located on rivers often make problems. As the cities grow 【小题7】 size and industries increase in number, the water in the rivers bees 【小题8】 (pollute) with chemicals and other materials. People are learning the 【小题9】 (important) of doing more to keep their rivers clean 【小题10】 they want to enjoy the benefits of this natural resource.cities
网友回答
(答案→)cities
解析：可联系答.案.网客服索取。