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下面是对铁的锈蚀条件的探究。因通常实验中铁生锈所需要时间较长，某实验小组设计了如图所示的改进实验。

(1)检查装置的气密性：连接好装置，关闭分液漏斗的旋塞，将C导管接入到装有水的烧杯中,微热甲装置，说明气密性良好的现象是___________________。

(2)反应开始后，甲装置中的反应现象：_______________________，MnO2的作用：__________________。

(3)4分钟后观察：A处铁丝依然光亮，B处铁丝表面灰暗，D处铁丝依然光亮，A、B处实验现象对比，可得出铁生锈与____________有关；B、D处实验现象对比说明：决定铁生锈快慢的一个重要因素是________________________。

答案

(1)C导管口有气泡冒出

(2)产生大量气泡    催化作用

(3)水    氧气的浓度

(1)由于甲装置内的空气受热时体积膨胀，若气密性良好，则C导管口有气泡冒出；(2)由于H2O2溶液在MnO2的催化作用下迅速分解，生成氧气，因此有气泡冒出；(3)A与B相比较，不同之处是B处的铁丝表面有水，且表面有铁锈生成，因此可得出铁生锈与水有关；B和D相比较，不同之处是B处氧气浓度大，故生锈所需时间比D短，所以表面有铁锈生成，说明铁生锈快慢与氧气的浓度有关。

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     At the beginning of the twentieth century, many people thought that the American family was falling
apart. A century later, we know that this was not the case. However, although the family is still alive in the United States, its size and shape were very different 100 years ago.
     In the late 1800s and early 1900s, there were mainly two types of families in the United States: the
extended and the nuclear. The extended family usually includes grandparents, parents, and children living
under the same roof. The nuclear family consists of only parents and children.
     Today there are many different kinds of families. Some people live in "traditional" families, that is, a
stay-home mother, a working father, and their own biological children. Others live in two-paycheck families, single-parent families, adoptive or foster, families, blended families (where men and women who were
married before marry again and combine the children from previous marriages into the new families),child
less families, and so on.
     What caused the structure of the family to change? In the early 1900s the birthrate began to fall and the divorce rate began to rise. Women were suddenly choosing to go to college and take jobs outside the
home. In the 1930s and 1940s, many families faced serious financial, or money problems during the Great Depression, when many people lost their jobs. During World War II(1939-1945),5 million women were
left alone to take care of their homes and their children. Because many men were at war, thousands of
these "war widows" had to go to work outside their home.
     During the next ten years, the situation changed. There were fewer divorces, and people married at a
younger age and had more children than the previous generation. It was unusual for a mother to work
outside the home during the years when her children were growing up. Families began leaving cities and
moving into single-family homes in the suburbs. The traditional family seemed to be returning.
     In the years between 1960s and 1990s, there were many important changes in the structure of the
family. From the 1960s to the early 1970s, the divorce rate doubled and the birthrate fell by half. The
number of single-parent families tripled, and the number of couples living together without being married
doubled again. In fact, the single-parent household, once unusual, has replaced the "traditional" family as
the typical family in the States. If we can judge from history, however, this will probably change again in the twenty-first century.
The Changes of the American Family
Main comparisonsContexts
Different  1  There were two  2    types of families in the past, namely, the extended and the   3  .
Nowadays   4  types of families can be seen than before.
  5  in different periods.In the 1900s and
1940s		Many of the women had to work outside due to the   6  of money., thus causing the fall of   7  and the rise of divorce rate.
In the 1950s
Divorce rate slided and there were more children. The families returned to be   8    again.
In the years between 1960s and 1990s Different types of families occurred. Traditional families are no longer the__9   ones in America.
A trend worth noting
Author's opinion on changesThe present structure is temporary.   10   from history, we know it will experience changes again in the near future.
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单项选择题

投用离心式压缩机润滑油系统的操作正确的是（）

A、高位油箱见回油后，继续保持快速上油阀开度，以排尽管路空气

B、润滑油过滤器回油阀应保持长流动，保持回油正常

C、避免润滑油氧化变质，投用的油箱隔离氮气压力越高越好

D、润滑油冷却器转动手柄开关要到位
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