题目

科学家侯德榜的主要成就是() A . 设计修建钱塘江大桥 B . 主持修建京张铁路 C . 发明了当时最先进的制碱法 D . 研制“两弹一星” 答案：C7、Rivers are one of our most important natural resources. Many of the world’s great _____31____ are located on rivers, and almost ____32_____ country has at least one river flowing through it that plays _____33_____ important part in the lives of its people.    Since the beginning of history, people _____34_____ (use) rivers for transportation. The longest one in the United States is the Mississippi, and the lifeline of Egypt is the Nile. _____35_____ transportation, rivers give water to drink, water for crops, and chances for fun and recreation for the people ____36___ live along their banks.    However, large cities and industries that are located on rivers often make problems. As the cities grow ____37_____ size and industries increase in number, the water in the rivers becomes _____38_____ (pollute) with chemicals and other materials. People are learning the _____39_____ (important) of doing more to keep their rivers clean ____40______ they want to enjoy the benefits of this natural resource.