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【简答题】
The petrochemical industry claims that chemical waste dumps pose no threat to people living near them. If this is true, then why do they locate the plants in sparsely populated regions. By not locating the chemical dumps in densely populated areas the petrochemical industry tacitly admits that these chemicals are potentially dangerous to the people living nearby. Which of the following, if true, would most weaken the author's argument? A. Funding through the environmental Super Fund to clean up poorly run waste dumps is reserved for rural areas only. B. Until chemical dumps are proven 100% safe, it would be imprudent to locate them were they could potentially do the most harm. C. Locating the dumps in sparsely populated areas is less expensive and involves less government red tape D. The potential for chemicals to leach into the water table has in the past been underestimated.
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【多选题】学前儿童科学教育内容的特点是()
A.
在引导学前儿童了解周围环境的同时,了解人体自身
B.
让学前儿童感受技术、崇尚科学
C.
在认识周围环境的同时,进行环境保护教育
D.
把认识个别物体的属性和认识物体的多样性结合起来
【单选题】如图所示回油节流调速回路,已知液压泵的的供油流量 q=25 L/min ,负载 F=40000N ,溢流阀调定压力 p Y =5.4MP ,液压缸无杆腔面积 A 1 =80cm 2 ,有杆腔面积 A 2 =40cm 2 ,液压缸工进速度υ =0.18m/min ,节流阀为薄壁孔, C q =0.62 。不考虑管路损失和液压缸的摩擦损失,试掌握计算步骤并计算后回答: 1 )液压缸工进时液压系统的效率...
A.
5.33%，10.8MPa，0.66m/min
B.
5.33%，5.4MPa，0.66m/min
C.
5.33%，2.7MPa，0.66m/min
D.
15.33%，5.4MPa，0.66m/min
【简答题】如图6-33b所示的回油节流调速回路，已知液压泵的供油量qp=25L／min，负载F=40000N，溢流阀调定压力Pp=5．4MPa，液压缸无杆腔面积A1=80×10-4m2，有杆腔面积A2=40×10-4m2，液压缸工进速度v=0．18m／min，不考虑管路损失和液压缸的摩擦损失，试计算： 1)液压缸工进时液压系统的效率。 2)当负载F=0时，活塞的运动速度和回油的压力。
【简答题】学前儿童科学教育内容选编的原则是()A科学性、启蒙性和系统性 B科学性、启蒙性、系统性和时代性 C科学性、启蒙性、系统性、时代性和地方性 D科学性、启蒙性、系统性、时代性、地方性和季节性
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