一组数据的方差S2=120[(x1-30)2+(x2-30)2+…+(xn-30

题型:填空题

问题:

一组数据的方差S2=
1
20
[(x1-30)2+(x2-30)2+…+(xn-30)2],则这组数据的平均数是 ______,n=______.
考点:平均数方差
题型:填空题

目前,某些科研机构研发了以餐饮废油(地沟油)和海藻为原料通过氢化、催化体系等加工生产生物航空煤油的技术,航空煤油燃烧会放出热量。下列有关分析错误的是

A.此项技术有助于丰富民用航空业的燃油来源

B.生物航空煤油的生产过程中没有发生化学变化

C.人类需要的大部分能量是由化学反应产生的

D.“地沟油”可以进行合理利用变废为宝

题型:填空题

相对于数据库系统,文件系统的主要缺陷有数据关联差、数据不一致性和 ( )

A.可重用性差

B.安全性差

C.非持久性

D.冗余性

题型:填空题

Televisions, stereos, telephones, and computers have changed the way we spend our time and what we know about the world. Some of the changes brought about by these material possessions have improved our way of life, but others have made it worse. Our young teenagers turn on the television, play the stereo, play games on the computer, talk on the telephone, and eat all the same time. This drives me right up the wall to instant insanity(精神失常).

However, teens of today place too great an importance on material property. They spend an average of several hours a day watching television, listening to stereos, playing on the computer, playing video games, and talking on the telephone. Families no longer watch television together and there is great lack of communication. Materialism is evident when an otherwise intelligent teenager drives their parents crazy, and into debt, when misusing communication equipment. Teens judge and admire other teens for what they own and have, rather than for what they are or what they can do. They no longer care about values, like honesty, integrity(正直), freedom, talent, quality and other values and morals.

However, good or bad, communication devices are here to stay. It is up to us, as parents, to stop our beloved teenagers from misusing and abusing our communication equipment and devices. We need to avoid the problems they present and to make the most of their opportunities they possess and hold for us all.

小题1:The writer’s attitude toward the modern material possessions is generally _____.

A.positive

B.negative

C.neutral

D.indifferent小题2:According to the writer, teens’ overuse of communication equipment can do harm to _____.

A.their own health

B.their own study

C.their own morality

D.their neighbors’ life小题3:The writer attributes (归咎) the unsatisfactory behavior of teens to _____.

A.teens’ too much free time

B.parents’ non-interference

C.inadequate school education

D.material property小题4:It can be inferred from the passage that the writer seems to be most annoyed at ______.

A.all the modern material possession

B.eating while talking on the phone

C.the decline in teens’ morality

D.all the communication equipment

题型:填空题

在一个固定容积的密闭容器中,可发生以下反应:A(g)+B(g)xC(g)符合下图(a)所示的关系(W(C)表示C的体积分数),由此推断关于图(b)的说法正确的是

A.P3>P4,y轴表示A的转化率                  B.P3<P4,y轴表示B的体积分数

C.P3<P4,y轴表示混合气体的平均相对分子质量   D.P3>P4,y轴表示混合气体的密度

题型:填空题

根据公务员法的规定,以下()类人员不属于公务员。

A.九三学社机关的工作人员

B.在国有企业工作的全国人大代表

C.基层检察院行政管理人员

D.政协办公厅工作人员

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