用如图的装置来测定空气中氧气的体积分数．（1）将燃烧匙内的_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题填空题

用如图的装置来测定空气中氧气的体积分数．

（1）将燃烧匙内的白磷点燃放人集气瓶中，观察到的现象是：______；

（2）反应停止一段时间后，打开弹簧夹，烧杯中的水会______；

（3）实验后发现测定的氧气体积分数低于

1

5

，请你分析实验误差的可能原因（写出其中一种即可）：______．

答案

（1）白磷燃烧的现象是产生大量白烟，放出热量；

（2）白磷燃烧消耗氧气，压强减小，因此反应停止一段时间后，打开弹簧夹，烧杯中的水会倒吸进入集气瓶，约占集气瓶体积的五分之一；

（3）进行此实验时，必须保证装置的气密性良好，红磷足量，装置冷却后再打开弹簧夹，否则会导致结测定的氧气体积分数低于五分之一．

故答案为：（1）产生大量白烟，放出热量；

（2）倒吸进入集气瓶，约占集气瓶体积的五分之一；

（3）红磷的量不足．

完形填空

Our Future Homes
　What kinds of homes will we live         the future? Nobody can be sure,         architects, and scientists are         new ideas now.
　　Some architects are thinking about          whole cities under huge glass domes. Of course, complicated heating and        systems will be necessary to control the climate in the domes.        , there will never be any rain      snow, and the temperature will be always        .
　　Perhaps everyone will live in vertical（立体的）       . High rises are so large that they can contain all the necessities of life. Since vertical cities will use        land than horizontal cities, and provide homes for more people, they will be       for small countries that have     populations.
Another idea that will be helpful to        countries (and island countries) is
the      city. Monaco has already built homes, stores, and offices         the water of the Mediterranean Sea. And a Japanese       has made a plan for constructing buildings on bridges over Tokyo Bay.
　　There are some people who think we will go back to living in       . But the caves of the future will be quite      the caves of the Stone Age. Computers will control light and climate. Farms and parks will be on the land      the cave city. When people want to go to the country or to a park, a short ride in       will take them there.

A．working out

D．comfortable

C．unnecessary

A．different from

B．similar with

D．the same as

C．an elevator

单项选择题

PageRank是一个函数，它对Web中的每个网页赋予一个实数值。它的意图在于网页的PageRank越高，那么它就（）。

A.相关性越高

B.越不重要

C.相关性越低

D.越重要