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  3. By the 1820s in the United States, when steamboats were common on western waters, these boats were mostly powered by engines bui

By the 1820s in the United States, when steamboats were common on western waters, these boats were mostly powered by engines bui

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问题     By the 1820s in the United States, when steamboats were common on western waters, these boats were mostly powered by engines built in the West (Pittsburgh, Cincinnati, or Louisville), and of a distinctive western design specially suited to western needs. The first steam engines in practical use in England and the United States were of low-pressure design. This was the type first developed by James Watt, then manufactured’ by the firm of Boulton and Watt. Steam was accumulated in a large, double-acting vertical cylinder, but the steam reached only a few pounds of pressure per square inch. It was low-pressure engines of this type that were first introduced into the United States by Robert Fulton. He imported such a Boulton and Watt engine from England to run the Clermont. But this type of engine was expensive and complicated, requiring many precision-fitted moving parts. The engine that became standard on western steamboats was of a different and novel design. It was the work primarily of an unsung hero of American industrial progress.
    Oliver Evans (1755—1819) was the self-educated son of a Delaware farmer. Evans early became obsessed by the possibilities of mechanized production and steam power. As early as 1802 he was using a stationary steam engine of high-pressure design in his mill. Engines of this type were not unknown, but before Evans they were generally considered impractical and dangerous. Within a decade the high-pressure engine, the new type had become standard on western waters. Critics ignorant of western conditions often attacked it as wasteful and dangerous. But people who really knew the Ohio, the Missouri, and the Mississippi insisted, with good reasons, that it was the only engine for them. In shallow western rivers the weight of vessel and engine was important; a heavy engine added to the problem of navigation. The high-pressure engine was far lighter in proportion to horsepower, and, with less than half as many moving parts, was much easier and cheaper to repair. The main advantages of low-pressure engines were safe operation and economy of fuel consumption, neither of which meant much in the West. (354 words)
In the 1820s, the steam engines used in the western America were______.
选项 A、of low-pressure design
B、of high-pressure design
C、created by Watt
D、manufactured by the firm of Boulton and Watt
答案B
解析 文章第一段第三句说，第一代轮船发动机是低压的，第二段开始叙说第二代蒸汽发动机。Evans根据西部河流的特点采用了高压设计，所以到了19世纪20年代，行驶在美国西部河流的蒸汽船都是高压设计的。
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