The definition of the standard kilogram is fundamentally imperfect.Getting the definition right is a challenge that has tried the patience and intelligence of scientists for decades.
Scientists use just seven basic units to define all the other quantities we use - quantities such as speed，density，or electric power.All of those basic units except the kilogram are themselves defined in terms of natural properties that are beyond human control.
For example，the standard second （time） is defined as a specific number of vibration of a type of radiation released by atoms of a special metal.The standard meter （length），in turn，is defined as the length of the path light travels in a vacuum during a specific fraction of a second.
Not so the kilogram.This orphan of the basic unit family is simply the mass of a small platinum-iridium alloy cylinder（鉑-銥合金筒）locked away by the international Bureau of Weighs & Measures in France.
Embarrassingly，the last time the copies were brought for a checkup in the 1980s，officials found that some copies had gained about 20 parts per billion in weight compared to the master cylinder since the previous checkup in the 1940s.This implies that the master cylinder itself may be an inconstant standard.
No one knows what causes the weight changes.But the uncertainty can't be tolerated when precision in research and some manufacturing now demands accuracy to a few parts per billion.
Several efforts in several different countries are under way to redefine the kilogram in terms of basic physical quantities such as counting the actual number of atoms of a specific substance in a kilogram or the electromagnetic force that balances a kilogram mass against gravity.
A project of the latter type at the NIST laboratories in Gaithersburg hopes eventually to define mass in terms of electrical units.So far，none of these redefinition projects has borne fruit.They require precision of measurement and control of experimental conditions.The slightest pollution，tiny vibrations，or other influences - even changes in weather - can ruin results.You've got to hand it to scientists who are willing to devote many years to such painstaking but fundamentally important research.
（1）Which of the following best paragraphs the sentences "Not so the kilogram." in paragraph 4？CC
A．The kilogram is not as accurate as the standard second.
B．The kilogram is not universally accepted in the world.
C．The kilogram is not defined in terms of natural properties.
D．The kilogram is not well defined as time and length.
（2）The author introduced the examination of copies of platinum-iridium alloy cylinder in the 1980s to indicate that CC.
A．the cause of weight changes had been found
B．such kind of checkups had been carried out regularly
C．the changes in weight challenged the definition of kilogram
D．the consequences of such changes were significant in research
（3）According to the passage，to define the weight of mass in terms of electrical units DD.
A．is one of the best methods to redefine the kilogram
B．has been accepted as the only possible redefinition project
C．is not as difficult as what people can understand
D．has been considered by some scientists as a better approach
（4）We can known from the passage that the redefinition of the kilogram is BB.
A．more important in keeping market honesty
B．worth years of scientists' painstaking research
C．the urgent requirement of business and manufacturing
D．bringing about important and fruitful results
【答案】C；C；D；B
【解答】
【點(diǎn)評(píng)】
聲明：本試題解析著作權(quán)屬菁優(yōu)網(wǎng)所有，未經(jīng)書面同意，不得復(fù)制發(fā)布。
發(fā)布：2024/5/27 14:0:0組卷：1引用：1難度：0.5
相似題
-
1．Hi Judy!
You often complain to me that you always buy goods unreasonably on sale promotion（促銷）and feel it shameful after going back to your school dormitory with new things not needed，considering all the money you spend is your parents' income．
In fact，this is a common phenomenon，called impulsive buying，a buying unplanned and hard to control．It usually happens when a store offers discounts（打折）or sales promotion-a special way used by stores to get more customers，which means you may fall into its traps even without notice．
Stores，with a good knowledge of customers' psychology（心理），make use of it to drive business．Avoiding all the impulsive buying is a hard thing．However，knowing our psychology behind it and reducing the times when influenced by sales promotion may be useful．So you should keep calm when facing the sales promotion by keeping in mind what you really need．
Find out the conditions where you are likely to buy things blindly．When seeing a dress advertised at 20% off，do not concentrate on the discount，but warn yourself against falling into the trap of "saving money''．
Besides，do not forget the long-term effects of your choice when meeting a sales promotion．Short-term benefits，like excited feeling just after buying items encourage impulsive buying．But the long-term costs such as waste of money and the sense of shame really annoy you．When seeing the advertisements，remember what you really want to buy originally and warn yourself of that terrible feeling．Only in this way can you save money for really needed things．
Yours，
Rachel
（1）Judy felt it a shame to．
A．complain to others about the poverty of her family
B．waste her parents' money on unneeded things
C．buy cheap things at lower prices or with less money
D．rely on her parents for further education
（2）Which of the following is true of impulsive buying according to Rachel？
A．It is designed by shops to draw customers' attention．
B．It can be brought under control with the help of stores．
C．It is planned by buyers with the purpose of saving money．
D．It is done by customers without considering its bad effects．
（3）In face of sales promotion Judy is advised to．
A．have belief in her own immediate decision
B．check the quality of the goods at low prices
C．stay calm by thinking about what she really needs
D．take the chance to learn more about stores tricks
（4）How do buyers usually feel in the long run after buying discounted things？
A．Regretful．
B．Thrilled．
C．Relaxed．
D．Sceptical．發(fā)布：2025/1/10 8:0:1組卷：4引用：2難度：0.6 -
2．English Schools There's no substitute for taking an English course in a high quality language school in an English-speaking country.Esl-lounge Student has partnered with some of the best language schools in the UK.Choose a school from below.We can offer discounts on English courses!
Burlington School，London
Burlington School is located in Parsons Green，15 minutes by underground from the centre of London.Our standard of teaching is high，with courses in General and Specialist English.The coffee bar is open all day serving freshly-cooked meals，and the school organises a range of social activities to complement （補(bǔ)充） the classes.Students live either in homestays or in one of our hostels.
See Burlington School courses and save 10%
University of Liverpool，English Language Centre
You can have confidence in the University of Liverpool，which is ranked in the top 1% of higher education institutions worldwide.While studying here，you will benefit from modern and dynamic English teaching methods in small classes of fewer than 16 students.
See University of Liverpool courses and save 12%
Interactive English School，Brighton
We are a small friendly school.Being a small school means we can cater for your individual needs more easily than larger schools can.All of our teachers are native speakers，qualified and experienced.Our prices are very affordable and start from ￡60 per week for fulltime courses of 20 lessons.
See Interactive English School courses and save 7%
New School of English，Cambridge
The New School of English is located in the beautiful city of Cambridge.The school is open all year and provides a range of English language courses for adults from all over the world（minimum age 16）.These courses cover General English as well as courses for professionals looking to focus on specific topic areas.They have a range of accommodation choices for students.
See New School of English courses and save 5%
（1）What can we know about Burlington School？
A．It is open all year.
B．It is located in London.
C．It provides no accommodation.
D．It offers no social practice classes.
（2）Which school offers the biggest discounts？
A．Burlington School.
B．New School of English.
C．University of Liverpool.
D．Interactive English School.
（3）How is New School of English different from the others？
A．It sets a strict age limit.
B．Its accommodation is optional.
C．Its teachers are qualified and experienced.
D．It offers General and Specialist English courses.發(fā)布：2025/1/6 16:30:6組卷：0引用：1難度：0.6 -
3．Ever since I graduated from high school I've worked in the factories surrounding my hometown every summer.However，making the transformation between school and full-time blue-collar work during the break never gets any easier.For a student like me who considers any class before noon to be unacceptable，getting to a factory by 6 o'clock each morning is suffering.My friends never seem to understand why I'm so relieved to be back at school or that my summer vacation has been anything but a vacation.
There are few people as self-confident as a college student who has never been out in the real world.People of my age always seem to overestimate the value of their time and knowledge.In fact，all the classes did not prepare me for my battles with the machine I ran in the plant，which would jam whenever I absent-mindedly put in a part backward or upside down.
The most stressful thing about blue-collar life is knowing your job could disappear over night.Issues like being laid off and overseas relocation had always seemed distant to me until my co-workers told me that the unit I was working in would shut down within six months and move to Mexico，where people would work for 60 cents an hour.
After working 12-hour shifts（輪班）in a factory，the other options have become only too clear. "This job pays well，but it's hell on the body，" said one co-worker. "Study hard and keep reading." she added.When I'm back at the university，skipping classes and turning in lazy re-writes seems too irresponsible after seeing what I would be doing without school.All the advice and public-service announcements about the value of an education that used to sound stale（陳腐的）now ring true.
My experiences in the factories have inspired me to make the most of my college years before I enter the real world for good.
（1）What does the author think of his summer holiday？
A．It was no holiday for him at all.
B．It brought him nothing but suffering.
C．It was a relief from his hard work at school.
D．It offered him a chance to make more friends.
（2）What can we infer about most college students？
A．They do better in the real world.
B．They are confident when they work.
C．They think too highly of themselves.
D．They are expert at handling machines.
（3）What is the biggest pressure for blue-collar workers？
A．A low income.
B．The lack of security.
C．An unstable location.
D．Less break.
（4）How did the working experiences change the author？
A．He became responsible for his work.
B．He learned to be more practical at work.
C．He began to respect blue-collar workers.
D．He came to appreciate his college education.發(fā)布：2025/1/6 16:30:6組卷：0引用：1難度：0.5