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【单选题】
By the 1820's 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 【21】______ practical use in England and the United States were 【22】______ low-pressure design. This was the type first 【23】______ by James Watt, then manufactured by the firm of Boulton and Watt. Steam was 【24】______ 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 【25】______ first introduced into the United States by Robert Fulton. He 【26】______ such a Boulton and Watt engine from England to run the Clermont. But this type of engine was ,expensive and complicated, 【27】______ many precision-fitted moving parts. The engine that became standard on western steamboats was of a different and 【28】______ design. It was the work primarily of an unsung hero of American industrial progress, Oliver Evans (1755-1819), the 【29】______ son of a Delaware farmer. Evans early became 【30】______ by the possibilities of mechanized production and steam power. As early as 1802 he 【31】______ a stationary steam engine of high-pressure design in his mill. Engines of this type were not 【32】______ , but before Evans they were generally considered 【33】______ and dangerous. Within a decade the high-pressure engine, the new type, had become standard on western waters. Critics 【34】______ of western conditions often attacked it as wasteful and dangerous. But people who really knew the Ohio, the Missouri, and the Mississippi 【35】______ , with good reasons, that it was the only engine for them. In 【36】______ western rivers the weight of vessel and engine 【37】______ important a heavy engine added to the problem of navigation. The high-pressure engine was 【38】______ 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 【39】______ of fuel consumption, 【40】______ of which meant much in the West.. 【21】
A.
on
B.
by
C.
for
D.
in
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A.
人们头脑中天生固有的
B.
人们主观自生的
C.
一定社会历史条件和经济关系的产物
D.
阶级矛盾和阶级斗争的产物
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A.
加强统筹协调
B.
改革规划管理体制
C.
加强体制改革
D.
规划确定的约束性指标具有法律效力
E.
协调发展
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A.
提高环境监管效能
B.
建立环境民主协商机制
C.
解决资源低价问题
D.
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A.
6
B.
7
C.
8
D.
9
【多选题】仓库害虫的生活习性包括:
A.
适应性强
B.
具有一定耐药性
C.
食性单一
D.
具隐蔽性
E.
繁殖力强
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A.
dans le passé
B.
aujourd'hui
C.
dans le futur
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A.
人们头脑中天生固有的
B.
人们主观自生的
C.
一定社会历史条件和经济关系的产物
D.
阶级矛盾和阶级斗争的产物
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A.
币值变动假设
B.
会计主体假设
C.
持续经营假设
D.
会计分期假设
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A.
运放处于线性工作状态
B.
输入输出函数呈线性关系
C.
输入端电压和电流呈线性关系
D.
输出端电压和电流呈线性关系
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