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【单选题】
化学兴趣小组的三位同学对蜡烛（主要成分是石蜡）及其燃烧进行了如下探究。 （1）他们观察蜡烛的燃烧，得出下列结论。请回答： 哪些是不需要燃烧就能观察到的现象（填字母）____ 哪些是需要燃烧才能观察到的现象（填字母）____ ａ．自顶端起约１ｃｍ以内的烛体是温的、柔软且易塑型； ｂ．原料是半透明、微臭、无味白色固体； ｃ．蜡烛顶端、烛心底部周围有无色液体，呈碗状存在 ｄ．一白色烛心贯穿中轴，并延长至蜡烛顶１ｃｍ ｅ．形状圆柱形，顶部为圆锥形尖出ｆ．烛心周围和上端呈明亮的黄色 ｇ．吹熄后，见烛心周围有白烟上升，并慢慢消失ｈ．质软，可用指甲刮出痕迹； ｉ．若风吹至蜡烛一边；另一边碗形顶端的蜡烛将熔成液体并沿烛体落下； ｊ．如受空气流的影响，火焰会闪动，且生出黑烟。 除此之外，燃烧时你还观察到的现象有（写两点）____，____。 （2）在探究蜡烛燃烧的过程中，他们发现罩在火焰上方的烧杯内壁被熏黑，你认为他们的以下做法中，不合适的是（ ）A.
反复试验，并观察是否有相同现象
B.
查找资料，了解石蜡的主要成分，探究生成的黑色固体是什么
C.
认为与本次实验目的无关，不予理睬
D.
询问老师或同学，讨论生成黑色固体物质的原因
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皮皮学刷刷变学霸
举一反三
【单选题】Learning effects:
A.
tend to be less significant when a technologically complex task is repeated.
B.
will be less significant in an assembly process involving 1,000 complex steps than in one of only 100 simple steps.
C.
typically disappear after a while, in spite of the complexity of the task.
D.
are more significant after two or three years of the introduction of a new process.
【单选题】It has been suggested that learning effects are important only during the start-up period of a new process and that they cease after two or three years. Any decline in the experience curve after such ...
A.
reduction in fixed costs.降低固定成本
B.
higher depreciation costs.更高的折旧成本。
C.
economies of scale.规模经济
D.
obsolescence.过时
【单选题】在风机盘管加新风空调系统中,从保证室内空气品质方面考虑,下列哪种新风送入方式较好
A.
新风单独送入室内
B.
A. 新风送入风机盘管回风箱中
C.
新风送入吊顶内
D.
新风送入走廊内
【简答题】What are learning effects? When are learning effects most significant? 学习效果如何?什么时候学习效果最显著?
【单选题】在风机盘管加新风空调系统中,从保证室内空气品质方面考虑,下列哪种新风送入方式较好?
A.
新风单独送入室内
B.
新风送入风机盘管回风箱中
C.
新风送入吊顶内
D.
新风送入走廊内
【单选题】Learning effects: 学习曲线效应
A.
tend to be less significant when a technologically complex task is repeated.当一项复杂的技术任务被重复时,显著性往往会降低。
B.
will be less significant in an assembly process involving 1,000 complex steps than in one of only 100 simple steps.在涉及1000个复杂步骤的装配过程中,其显著性要小于只涉及100个简单步骤中的一个。
C.
typically disappear after a while, in spite of the complexity of the task.通常会在一段时间后消失,尽管任务很复杂。
D.
are more significant after two or three years of the introduction of a new process在两到三年之后引入一个新的流程时更显著。
【单选题】Learning effects:
A.
result in unit manufacturing costs increasing by a certain amount each time output is increased.
B.
suggest that production costs increase because of increasing labor productivity.
C.
are more significant when simple steps in an assembly process are performed over and over again.
D.
are more significant when a technologically complex task is repeated.
E.
lead to diseconomies of scale.
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