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【简答题】
钠是一种非常活泼的金属，用小刀切一小块钠投入到蒸馏水的烧杯中（图a），可以看到钠块浮在水面上，与水发生剧烈反应，反应放出的热量使钠熔化成银白色的小球，甚至使生成的气体发生燃烧．如果在盛蒸馏水的烧杯中先注入一些煤油，再投入金属钠，可以看到金属钠悬浮在煤油和水的界面上（如图b），同样与水发生剧烈反应，生成氢氧化钠和另一种单质气体，但不发生燃烧．试根据以上叙述，解答下列问题： （1）钠与水反应的化学方程式是______； （2）图b中，钠与水发生反应，但不发生燃烧现象，这是因为______；钠悬浮在煤油和水的界面上，这现象说明了（从物理性质出发）______．
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举一反三
【单选题】Why do you think students feel bored in class?
A.
Because teachers can be cheated easily.
B.
Because lectures are very boring.
C.
Because students have little influence on and responsibility for their own education.
D.
Because class assignments are very easy.
【简答题】Learn to relax. Overwork is the main reason why so many students feel tired. Cut down some of the jobs you need to do each day so that you only do the most important things well. Leave time for activi...
【简答题】Learn to relax. Overwork is the main reason why so many students feel tired and stressed. Cut down some of the jobs you need to do each day so that you can only focus on the most important things. Lea...
【单选题】The term control is highly—and unjustifiably—unpopular. Some of its unpopularity can be traced to educational and philosophical writings that have addressed issues of freedom, self- determination, sel...
A.
unjustified control
B.
unpopularity
C.
liberal and permissive educational methods
D.
deliberate exercise of restrictions
【单选题】Public relations practice is the deliberat e, planned and sustained effort to establish and maintain mutual understanding between an organization and its public.
A.
complete
B.
related
C.
intentional
D.
active
【简答题】阅读理解。 Learn to relax. Overwork is the main reason why so many students feel tired and stressed (紧张). Cut down some of the jobs you need to do each day so that you can only focus on the most important ...
【简答题】法律的运行是一个从创制、实施到实现的过程。这个过程主要包括( )、( )、( )、( )等环节。
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