税率、税收收入和经济增长之间存在着相互依存、相互制约的关系，从理论上说应当存在一种兼

生物体能进行呼吸，绝大数生物需要从外界吸入______，呼出______；植物也能呼吸，它吸收空气中的二氧化碳和水，在______中进行光合作用，同时释放出______．

假设人造卫星绕地球做匀速圆周运动，当卫星绕地球运动的轨道半径增大到原来的2倍时，则有（　　）

A．卫星运动的线速度将减小到原来的一半

B．卫星所受的向心力将减小到原来的四分之一

C．卫星运动的周期将增大到原来的2倍

D．卫星运动的线速度将减小到原来的

阅读理解

    Sadness is unpleasant, and in a society where personal happiness is prized above all else, there is little

tolerance for falling in despair.Especially now we've got drugs for getting rid of sad feelings-whether it's

after losing a job, the breakup of a relationship or the death of a loved one.So it's no surprise that more

and more people are taking them.

     But is this really such a good idea?A growing number of voices from the world of mental health

research are saying it isn't.They fear that the increasing tendency to treat normal sadness as a disease is

playing fast and loose (行为轻率). Sadness, they argue, serves a useful purpose-and if we lose it, we

lose out.Yet many psychiatrists (精神病医生) insist not.Sadness has a nasty habit of turning into

depression (抑郁症), they warn.Even when people are sad for good reason, they should take drugs to

make themselves feel better.

     So who is right?Is sadness something we cannot live without or something horrible never to touch?

     There are lots of ideas about why feeling sad should become part of human life.It may be a

selfprotection strategy, as other primates (灵长类) also show signs of sadness.A losing monkey that

doesn't show sadness after it loses a fight may be seen as continuing to challenge the winning monkey-and

that could result in death.

     In humans, sadness has a further function:we may display sadness as a form of communication.By

acting sad, we tell other community members that we need support.

     Then there is the idea that creativity is connected to dark moods.There are plenty of great artists,

writers and musicians who have suffered from depression or disorder.Scientists find that people with

signs of depression perform better at a creative task, and that negative moods make people think deeply

over the unhappy experience, which allows creative processes to come to the front.There is also evidence

that too much happiness can be bad for your career.A doctor found that people who scored 8 out of 10

on a happiness test were more successful in income and education than 9s or 10s.The happiest people

lose their willingness to make changes to their lives that may benefit them.

1. The underlined word "this" refers to________.

A. taking drugs  

B. falling in despair

C. losing a job  

D. feeling sad

2. The author believes sadness is________.

A. a good thing for people's health

B. something horrible never to touch

C. a necessary function of humans

D. always to be treated as depression

3. Some animals show their sadness in order to________.

A. cheat their enemy  

B. protect themselves

C. comfort the loser  

D. challenge the winner

4. We can infer from the last paragraph that________.

A. people with great creativity tend to be happier

B. unhappy experiences contribute to a greater career

C. too much happiness can be bad for your career

D. the happiest people are the most successful ones

在气动PI调节器中，为获得积分作用，应采用（）

A.弹性气宣的反馈

B.节流分压器的正反馈

C.节流盲宣的正反馈

D.节流盲室的负反馈

如图所示该安全标志表示的意思是（）。

A.注意安全

B.当心火灾

C.当心爆炸

D.当心腐蚀