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 (铂-铱合金筒) 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(精密度) 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 paraphrases the sentence “Not so the kilogram.” in paragraph 4?
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.Which of the following can NOT be concluded from the passage?
A.Experiments are being carried out to redefine the kilogram.
B.The uncertainty in the standard kilogram can seriously affect some research.
C.The redefinition of the standard kilogram is quite complicated.
D.Scientists will achieve success in redefining the kilogram in the near future.
3.According to the passage, to define the weight of mass in terms of electrical units _______.
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 simple as what people can understand
D.has been considered by some scientists as a better approach
4.We can know from the passage that the redefinition of the kilogram is _________.
A.more important in keeping market honesty
B.worth years of scientists’ painstaking research
C.the urgent requirement of business and manufacturing.
D.bring about important and fruitful results
The beauty, majesty, and timelessness of a primary rainforest are indescribable. It is impossible to ______ on film, to describe in words, or to explain to those who have never had the awe-inspiring experience of standing in the heart of a primary rainforest.
Rainforests have ______ over millions of years to turn into the incredibly complex environments they are today. Rainforests represent a store of living and ______ renewable natural resources that for eons, by virtue of their richness in both animal and plant species, have ______ a wealth of resources for the survival and well-being of humankind. These resources have included basic food supplies, clothing, shelter, fuel, spices, industrial raw materials, and medicine for all those who have lived in the majesty of the forest. ______, the inner dynamics of a tropical rainforest is an intricate and fragile system. Everything is so ______ that upsetting one part can lead to unknown damage or even destruction of the whole. Sadly, it has taken only a century of human intervention to destroy what nature designed to ______ forever.
The scale of human _____ on ecosystems everywhere has increased enormously in the last few decades. Since 1980 the global economy has tripled in size and the world population has increased by 30 percent. Consumption of everything on the planet has risen——at a cost to our ______. In 2001, The World Resources Institute estimated that the demand for rice, wheat, and corn is expected to grow by 40% by 2020, increasing irrigation water demands by 50% or more. They further reported that the demand for wood could double by the year 2050; ______, it is still the tropical forests of the world that supply the bulk of the world's demand for wood.
In 1950, about 15 percent of the Earth's land surface was covered by rainforest. Today, more than half has already gone up in ______. In fewer than fifty years, more than half of the world's tropical rainforests have fallen ______ to fire and the chain saw, and the rate of destruction is still accelerating. Unbelievably, more than 200,000 acres of rainforest are burned every day. That is more than 150 acres lost every minute of every day, and 78 million acres lost every year! More than 20 percent of the Amazon rainforest is already gone, and much more is severely threatened as the destruction continues. It is estimated that the Amazon alone is vanishing at a rate of 20,000 square miles a year. If nothing is done to curb this ______, the entire Amazon could well be gone within fifty years.
Massive ______ brings with it many ugly consequences-air and water pollution, soil erosion, malaria epidemics, the release of carbon dioxide into the atmosphere and the ______ of biodiversity through extinction of plants and animals. Fewer rainforests mean less rain, less oxygen for us to breathe, and an increased threat from global warming.
1.A.present B.capture C.claim D.prove
2.A.changed B.evolved C.expanded D.existed
3.A.energizing B.healing C.isolating D.breathing
4.A.contributed B.stored C.reduced D.affected
5.A.However B.Furthermore C.Therefore D.Otherwise
6.A.active B.sensitive C.interdependent D.delicate
7.A.restore B.support C.revive D.last
8.A.pressure B.power C.concern D.strength
9.A.existence B.ecosystem C.planet D.survival
10.A.unfortunately B.consequently C.naturally D.similarly
11.A.store B.food C.smoke D.wealth
12.A.subject B.down C.apart D.victim
13.A.trend B.practice C.decrease D.attitude
14.A.destruction B.industrialization C.modernization D.deforestation
15.A.appearance B.explosion C.loss D.increase
Directions: After reading the passage below, fill in the blanks to make the passage coherent and grammatically correct. For the blanks with a given word, fill in each blank with the proper form of the given word; for the other blanks, use one word that best fits each blank.
Living Jewels
Before I went to the British Koi Keepers Annual Show, I didn’t understand 1. people could take fish so seriously. However, the more I learned about koi, the more interested became. As one expert told me, "Collecting koi is far more addictive than you might think. They’re as beautiful as butterflies and very calming to watch." Freddie Mercury, the lead singer of Queen, would have agreed the pool in his specially-built Japanese garden was home to 89 koi,2. cost up to $10,000 each.
At the show I met koi enthusiast Jean Kelly. “Koi are getting more and more expensive,” she told me. “One recently sold for $250,000.” I was shocked that's almost as much as I paid for my house. Well, that was a record,3.(admit) Jean. The normal price is nowhere near as high as that.
Nevertheless, serious collectors can pay up to $15,000 for a fully 4.(grow) koi, which is nearly as expensive as a new luxurious car, and the bigger they are, the more they cost. The cheapest I 5. find was $75 each, but they were only about twice as big as my goldfish.
Jean wasn’t impressed by one of the koi on sale either. “Actually, these koi aren’t any nicer than 6.,” she commented. “7. they are slightly bigger than the ones I’ve got, I paid considerable less than this.”
I wasn’t quite as enthusiastic as Jean, but I did consider8.(buy) one. Then I remembered that all but 5 of Freddie Mercury's koi died when someone accidentally turned off the electricity supply to their pool. Jean assured me that with all the new equipment available the survival rate was getting better and better, and that looking 9.koi was no harder than taking care of any other pet. However, in the end I decided to stick with my goldfish. They’re not nearly as beautiful as koi ——but they’re a great deal cheaper 10.(replace) !
Directions: After reading the passage below, fill in the blanks to make the passage coherent and grammatically correct. For the blanks with a given word, fill in each blank with the proper form of the given word; for the other blanks, use one word that best fits each blank.
Space is a dangerous place, not only because of meteors (流星) but also because of rays from the sun and other stars. The atmosphere again acts 1. our protective blanket on earth. Light gets through, and this is essential for plants 2.(make) the food which we eat. Heat, too, makes our environment endurable. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun 3. (screen) off. As soon as men leave the atmosphere, they are exposed to this radiation but their spacesuit or the walls of their spacecraft,4. they are inside, do prevent a lot of radiation damage.
Radiation is 5.(great) known danger to explorers in space. The unit of radiation is called "rem". Scientists have reason to think that a man can put up with far more than 0.1 rem without 6.(damage); the figure of 60 rems has been agreed on. The trouble is 7. it is extremely difficult to be sure about radiation damage - a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered 8. the birth of deformed children or even grandchildren. Missions of the Apollo flights have had to cross belts of high radiation and, during the outward and return journeys, the Apollo crew accumulated (积累) a large amount of rems. So far, no dangerous amounts of radiation have been reported, but the Apollo missions have been quite short. We simply don't know yet 9. men are going to get on when they spent weeks and months outside the protection of the atmosphere, working in a space laboratory. Drugs might help to decrease the damage 10.(do) by radiation, but no really effective ones have been found so far.
阅读下面短文，根据其内容写一篇60词左右的内容概要。
Once upon a time, eating alone was just that: sitting down in a restaurant on one’s own and eating a meal. Everyone did it sometimes, and when they did so they might be a little embarrassed. To eat alone might suggest that you didn’t have any family or friends, or didn’t like people. There was a kind of shame attached to it. Nowadays, however, there is more and more solitary(独自的) eating.
People choose to eat alone for various reasons. “Foodies”—people who have a passionate interest in different cuisines(美食)—do it because all they need for their pleasure is the chance to eat good food. They don’t want company or conversation, but only the joy of eating some special dish.
Other people eat alone because it’s simply practical for them to do so. For instance, it’s estimated that nearly a third of all the customers of fast-food restaurants eat alone. They are served with their food fast, eat it fast and then leave fast—because they have a meeting to make or a child to pick up from school.
But for others, the appeal of eating alone is quite different. It’s an experience of freedom. For the hour that it takes to have a meal, they can forget all the pressures of their lives. For a brief window, they don’t have to deal with their family or job. They can relax and let their mind wander. Maybe they will bring a book, a newspaper or perhaps they will shyly spy on the people around them. Part of the appeal of this new trend is surely that a meal taken alone is like a little holiday from the busyness of modern life, in which we have so much to do all the time. David Annand, editor of US-based Conde Nast Traveler magazine, who delights in dining alone, speaks of his pleasure in the “rhythm of a meal in a restaurant—its ebb and flow(人来人往), the regular arrival and departure of the waiter.” This restaurant rhythm allows him and others, he writes, to sit back, observe, and think.
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假设你是李华。在刚结束的中学生英语演讲比赛中获得了第一名。准备比赛期间， 你得到了外教James的指导和帮助。请你根据以下要点提示给外教James写一封邮件。内容 包括：
1. 获奖的消息
2. 外教的帮助
3. 感恩的心情
注意：
1. 词数 80 左右；
2. 可适当增加细节，以使行文连贯。
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