单项选择题

某容器中的混合气体含有甲烷、乙烷。甲烷的爆炸下限为5.O％，上限为15.O％；乙烷的爆炸下限为2.9％，上限为13.0％。动火环境中可燃气体的浓度不得超过（　　）。

A.2％
B.1％
C.0.5％
D.0.2％
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请根据表二和文字资料回答下列问题。表二：城乡家庭消费水平和消费结构比较[*]一般来说，恩格尔系数可以衡量家庭生活水平状况，但在调查中发现了低收入家庭恩格尔系数比中低和中等收入家庭恩格尔系数低的特殊情况。调查结果显示，家庭消费率明显偏低。由“表二：城乡家庭消费水平和消费结构比较”分析得出：城乡居民家庭消费差异和问题主要是( )。D.家庭消费率总体偏低，消费率随收入提高而边际递减
A.城乡家庭消费水平差异较大，消费结构差异明显
B.教育、医疗等发展型消费呈刚性特点
C.低收入家庭生活质量受到影响
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Learning disabilities are very common. They 【21】______ perhaps 10 percent of all children. Scientists now know there are many different kinds of learning disabilities and that they are 【22】______ by many different things. There is no longer any 【23】______ that all learning disabilities 【24】______ differences in the way the brain is organizeD.Since there is no 【25】______ sign of the disorder, some researchers began looking at the brain itself to learn what might be wrong.In one study, researchers 【26】______ the brain of a learning-disabled person. They found two unusual things. One 【27】______ cells in the left side of the brain, which control languagE.These cells 【28】______ are white, in the learning disabled person, 【29】______ , these cells were gray. The researchers also found that many of the nerve cells were not in a line the 【30】______ they should have been. The nerve cells were mixed together.The study was carded out 【31】______ the guidance of Norman Geschwind, an expert on learning disabilities. Doctor Geschwind 【32】______ that learning disabilities resulted mainly from problems in the left side of the brain, and this part of brain failed to develop normally. Probably, he said, nerve cells there did not connect 【33】______ they shoulD.So the brain was like an electrical device in which the wires were 【34】______ .Other researchers did not examine brain 【35】______ Instead, they measured the brain's electrical activity and made a map of the electrical 【36】______ . Frank Duffy experimented with this 【37】______ and found large differences in the brain activity of normal children and those with reading problems. The differences appeared 【38】______ the brain. Doctor Duffy said his research is 【39】______ that reading disabilities involve 【40】______ to a wide area of the brain, not just the left sidE.【21】A.influenceB.effectC.affectD.shape
A.B.
C.
D.
E.
【21】
A.influence
B.effect
C.affect
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