某单位青年职工、中年职工、老年职工的人数之比为7:5:3,为了了解该单位职工的健

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问题:

某单位青年职工、中年职工、老年职工的人数之比为7:5:3,为了了解该单位职工的健康情况,用分层抽样的方法从中抽取样本.若样本中的青年职工为14人,则样本容量为(  )
A.14B.30C.35D.25
考点:分层抽样
题型:选择题

(15分)硫酸厂用煅烧黄铁矿(FeS2)来制取硫酸,实验室利用硫酸厂烧渣(主要成分是Fe2O3及少量FeS、SiO2)制备绿矾.

⑴SO2和O2反应制取SO3的反应原理为:2SO2+O22SO3,在一密闭容器中一定时间内达到平衡.

①该反应的平衡常数表达式为:                  

②该反应达到平衡状态的标志是       

A.v(SO2)=v(SO3)        B.混合物的平均相对分子质量不变

C.混合气体质量不变    D.各组分的体积分数不变

⑵某科研单位利用原电池原理,用SO2和O2来制备硫酸,装置如图,电极为多孔的材料能吸附气体,同时也能使气体与电解质溶液充分接触.

 

①B电极的电极反应式为              

②溶液中H+的移动方向由     极到     极;(用A、B表示)

⑶测定绿矾产品中含量的实验步骤:

a.称取5.7 g产品,溶解,配成250 mL溶液

b.量取25 mL待测液于锥形瓶中

c.用硫酸酸化的0.01 mol/L KMnO4溶液滴定至终点,消耗KMnO4溶液体积40 mL

根据上述步骤回答下列问题:

①滴定时发生反应的离子方程式为(完成并配平离子反应方程式).

  Fe2++  +            ——  Fe3++  Mn2++          

②用硫酸酸化的KMnO4滴定终点的标志是               

③计算上述产品中FeSO4·7H2O的质量分数为           

题型:选择题

以下两图分别表示甲、乙两个生态系统的食物网,据图回答下题:

1.甲生态系统的食物网中属于生产者的是

A.蛇          B.草      C.猫头鹰      D.鼠

2.若人类对两食物网中的鼠大量捕杀,则受到影响最严重的生态系统是

A.甲生态系统

B.乙生态系统

C.甲、乙两生态系统受影响程度相同

D.无法判断

3.乙生态系统中猫头鹰和蛇的关系是

A.捕食 B.竞争          C.捕食和寄生  D.捕食和竞争

4.乙生态系统中蛇的生命活动所需能量归根结底来源于

A.鼠  B.草      C.兔   D.阳光

题型:选择题

利用市场信息最重要的素质是()。

A.想象力

B.注意力

C.勤奋态度

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×年7月是地球近几百年来最热的一个月份。正因为天气太热,人们纷纷涌向海滨,为当地的旅游业带来了很好的发展机会。产生这种影响的环境属于()。

A、政治环境

B、社会文化环境

C、经济环境

D、自然环境

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An awkward-looking character such as Cyrano de Bergerac might sniff at the suggestion, but recent scientific research shows beauty, brains and brawn may in fact all be allied, writes Dr Raj Persaud.

(46) Psychologists have concluded that we may be drawn to the stereotypically attractive because of what their faces reveal about their intelligence and success in later life. In American, research led by Professor Leslie Zebrowitz, of Brandeis University, has shown an association between facial attractive and IQ. Strangers briefly exposed to a target’s face were able to correctly judge intelligence at levels significantly better than chance.

The same team also researched how a person’s attractiveness might bear relation to their intelligence. They found that good-looking people did better in IQ tests as they aged. (47) Their research sought to prove that how a person perceived himself and was perceived by others predicted how intelligent he apparently became more accurately than his past intelligence. (48) Perhaps because the more attractive people were treated as more intelligent, they ended up having more stimulating and, therefore, intelligence-enhancing lives.

Does this mean that your face really could be your destiny Sociologists Dr Ulrich Mueller and Dr Allan Mazur, of the University of Marburg in Germany, recently analyzed the final year photographs of the 1950 graduates of West Point in the United States. Dominant facial appearances turned out to be a consistent predictor of later-rank attainment:

Again, they believed there could be a self-fulfilling effect. (49) Because some men looked more authoritative, they naturally drew respect and obedience from others which, in turn, assisted their rise through the ranks.

A team at the Royal College of Surgeons in Dublin has been investigating the sensitive subject of links between physical and mental abnormalities. Led by Doctors Robin Hennessy and John Waddington, the team used a new laser surface-scanning technique to make a 3-D analysis of how facial shape might vary with brain structure. Their findings showed that in early fetal life, brain and face development are intimately connected. From this they concluded that abnormalities in brain elaboration probably also affect face development.

This, according to them, explains the striking facial features of some one with Down’s syndrome. (50) Using similar techniques, the team also demonstrated how other disorders linked to brain aberrations could be associated with facial alterations.

So the very latest scientific research suggests that nobody should try to look too obviously different from average.

(49) Because some men looked more authoritative, they naturally drew respect and obedience from others which, in turn, assisted their rise through the ranks.

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