Today, most countries in the world have canals. Many countries have built canals

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问题 Today, most countries in the world have canals. Many countries have built canals near the coast, and parallel 【C1】______ the coast. Even in the twentieth century, goods can be moved more cheaply by boat than by any other 【C2】______ of transport. These 【C3】______ make it possible for boats to travel 【C4】______ ports along the coast without being 【C5】______ to the dangers of the open. Some canals, such as the Suez and the Panama, save ships weeks of time by making their 【C6】______ a thousand miles shorter. Other canals permit boats to reach cities that are not 【C7】______ on the coast; still other canals 【C8】______ lands where there is too much water, help to 【C9】______ fields where there is not enough water, and 【C10】______ water power for factories and mills. The size of a canal. 【C11】______ on the kind of boats going through it. The canal must be wide enough to permit two of the largest boats using it to 【C12】______ each other easily. It must be deep enough to leave about two feet of water 【C13】______ the keel of the largest boat using the canal. When the planet Mars was first 【C14】______ through a telescope, people saw that the round disk of the planet was crises-crossed by a 【C15】______ of strange bluegreen lines. These were called "canals" 【C16】______ they looked the same as canals on earth 【C17】______ are viewed from an airplane. However, scientists are now 【C18】______ that the Martian phenomena are really not canals. The photographs 【C19】______ from space-ships have helped us to 【C20】______ the truth about the Martian "canals". [br] 【C14】

选项 A、studied
B、researched
C、surveyed
D、observed

答案 D

解析 词义辨析题,表示“用…观测”,要用动词observe,所以D正确,study和research指“系统研究”, survey指“调查,检查”,均排除
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