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【简答题】
在各地农村的“村村通”建设中，推土机发挥了重要作用。 如图所示是TY160型履带式推土机，其发动机额定功率为120kW，质量为1.5×10 4 kg，每条履带与地面的接触面积为1.25m 2 。取g=10N/kg，求： （1）推土机安装履带主要是为了____________，履带上凸出的棱的作用是________________________。 （2）推土机的“心脏”是柴油机，柴油机工作过程中_____冲程将内能转化为机械能。 （3）推土机对水平地面的压强； （4）求当推土机以额定功率在的场地上以5.4 km/h的速度匀速前进时推土机所受到的阻力。 （5）若推土机把一块质量为2.4m 3 的石块沿斜坡推到高5m的山坡上，则推土机对石块做功为多少？（石块的密度为2.5×10 3 kg / m 3 ）
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【单选题】What is not the reason for adult moving back home according to researchers of US populations?
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Aging grandparents would eschew.
B.
Childbearing without matrimony.
C.
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wa s haile d b y Thoma s Rober t Malthu s a s th e ke y t o futur e economi c growth.
B.
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D.
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A.
the population growth rates in Thailand will have increased
B.
there will be a disproportionate number of older people
C.
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A.
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B.
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C.
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D.
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A.
We raise productivity and produce more food.
B.
We are willing to eat less food and use less material.
C.
We find another planet to live on.
D.
The developed world is willing to help the underdeveloped world.
查看完整题目与答案
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A.
little
B.
marked
C.
much
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lot
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【单选题】_____ the rising birth rate and immigration, the declining death rate also resulted in the population growth. [     ]
A.
In terms of
B.
In addition to
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In consequence of
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A.
laughing at
B.
being laughed at
C.
laughed at
D.
having been laughed at
查看完整题目与答案