科目: 來源:期末題 題型:閱讀理解
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科目: 來源:期末題 題型:閱讀理解
Can people change their skin colour without suffering like pop king Michael Jackson? Perhaps yes.
Scientists have found the gene that determines skin colour.
The gene comes in two versions, one of which is found in 99 per cent of Europeans. The other is
found in 93 to 100 per cent of Africans, researchers at Pennsylvania State University report in the latest
issue of Science.
Scientists have changed the colour of a dark-striped zebrafish to uniform gold by inserting a version
of the pigment (色素) gene into a young fish. As with humans,zebrafish skin colour is determined by
pigment cells, which contain melanosomes (黑色素). The number, size and darkness of melanosomes
per pigment cell determines skin colour.
It appears that, like the golden zebrafish,light-skinned Europeans also have a mutation (變異) in the
gene for melanosome production. This results in less pigmented skin.
However, Keith Cheng leader of the research team, points out that the mutation is different in human
and zebrafish genes.
Humans acquired dark skin in Africa about l.5 million years ago to protect bodies from ultra-violet rays
of the sun (太陽光紫外線), which can cause skin cancer.
But when modern humans leave Africa to live in northern latitudes, they need more sunlight on their
skin to produce vitamin D. So the related gene changes, according to Cheng.
Asians have the same verslon of the gene as Africans, so they probably acquired their light skin through
the action of some other gene that affects skin colour, said Cheng.
The new discovery could lead to medical treatments for skin cancer. It also could lead to research into
ways to change skin colour without damaging it like chemical treatment did on Michael Jackson.
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科目: 來源:期末題 題型:閱讀理解
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科目: 來源:同步題 題型:完形填空
完形填空。 | ||||
Earthquakes are 1 ; thousands of them happen each day. But most are too weak to feel. During a 2 earthquake, there is often a great noise first. Then the earth 3 terribly; many houses 4 down. Railway tracks break and trains go 5 lines; a great many factories are 6 ; thousands of deaths are caused, and many more lose homes... 7 the great damage and deaths caused by the earthquake 8 , other disasters such as fires often 9 . More buildings are destroyed and more 10 are caused. It is well known of the 11 of a possible earthquake, and for centuries man has been making researches on earthquakes. More than 2,000 years ago, 12 , a Chinese scientist named Zhang Heng 13 a machine which could find out from which 14 the seismic (地震的) waves had come, and this machine is still 15 by scientists today. Now we know much more about earthquakes and 16 they happen, but we still cannot 17 exactly when and where an earthquake will happen, and cannot 18 it from happening. So earthquakes are among the 19 disasters in the world. No one can stop natural earthquakes. 20 , scientists can help stop earthquakes from destroying whole cities and causing too many deaths. | ||||
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科目: 來源:期末題 題型:完形填空
完形填空。 | ||||
One student took a box of chicken to class. Another carried on a cell-phone 1 and still another whistled loudly every time the 2 turned his back. Reform school? No, College. More and more, professors say, they are coming across 3 students in their classrooms. Many of today's young scholars (學(xué)者) arrive late, leave 4 , talk loud or take care of personal 5 such as paying bills during class. Why are the students behaving badly? "Because they can," said a student of University of North Texas. "A lot of the time, the professors let them get 6 with it." Some educators say it is time to bring politeness back to their classrooms-and even 17 taking some of the blame for bad behavior. They say that rude students are by no means the majority but that one of them can ruin an entire 8 . People are 9 when they learn that impolite behavior is becoming more and more common in 10 education, says Dr. Gerald Amanda, a counselor at City College of San Francisco. They 11 some high school students to misbehave but think those who get to 12 will behave more politely. Dr. Amanda believes that society in 13 has become more tolerant (容忍的) of rude behavior and 14 people in power, including professors, no longer 15 standards for 16 . That leads to a growing imprudence (輕率行為) 17 some college students. "There's a great 18 of bad behavior in the world around them, and young people see it and 19 disrespect," said Dr. Amanda, 20 that sometimes students "have no idea that they are being rude". | ||||
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科目: 來源:期末題 題型:閱讀理解
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科目: 來源:同步題 題型:閱讀理解
選做題。請認(rèn)真閱讀下列短文,并根據(jù)所讀內(nèi)容在文章后表格中的空格里填入一個最恰當(dāng)?shù)膯卧~。 | |||||||||||
For more than twenty years scientists have been seeking to understand the mystery of the "sixth sense" of direction. By trying out ideas and solving problems one by one, they are now getting closer to one answer. One funny idea is that animals might have a built-in compass (指南針). Our earth itself is a big magnet (磁體). So a little magnetic needle that swings freely lines itself with the big earth magnet to point north and south. When people discovered that idea about a thousand years ago and invented the compass, it allowed sailors to navigate (航海) on ocean voyages, even under cloudy skies. Actually the idea of the living compass came just from observing animals in nature. Many birds migrate twice a year between their summer homes and winter homes. Some of them fly for thousands of kilometers and mostly at night. Experiments have shown that some birds can recognize star patterns. But they can keep on course even under cloudy skies. How can they do that? A common bird that does not migrate but is great at finding its way home is the homing pigeon. Not all pigeons can find their way home. Those that can are very good at it, and they have been widely studied. One interesting experiment was to attach little magnets to the birds' heads to block their magnetic sense-just as a loud radio can keep you from hearing a call to dinner. On sunny days, that did not fool the pigeons. Evidently they can use the sun to tell which way they are going. But on cloudy days, the pigeons with magnets could not find their way. It was as if the magnets had blocked their magnetic sense. Similar experiments with the same kind of results were done with honeybees. These insects also seem to have a special sense of direction. In spite of the experiments, the idea of an animal compass seemed pretty extraordinary. How would an animal get the magnetic stuff for a compass? An answer came from an unexpected source. A scientist was studying bacteria that lived in the mud of ponds and marshes. He found accidentally little rod-like bacteria that all swam together in one direction-north. Further study showed that each little bacterium had a chain of dense particles inside, which proved magnetic. The bacteria had made themselves into little magnets that could line up with the earth's magnet. The big news was that a living thing, even a simple bacterium, can make magnetite. That led to a search to see whether animals might have it. By using a special instrument called magnetometer, scientists were able to find magnetite in bees and birds, and even in fish. In each animal, except for the bee, the magnetic stuff was always in or close to the brain. Thus, the idea of a built-in animal compass began to seem reasonable. | |||||||||||
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科目: 來源:同步題 題型:閱讀理解
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科目: 來源:同步題 題型:閱讀理解
閱讀理解。 | ||
to send their signals to faraway places. This was because most cities had only one antenna tower for mobile phones. Today's mobile phones are small and easy to use. Now most cities have a lot of antenna towers, not just one. This means that each mobile phone doesn't have to send its signal far away, so they don't need to be so powerful. Mobile phones today use small batteries. A large city, where lots of mobile phones are used, can have hundreds of towers. Do you know what use a mobile phone has? Yes, you can use it to do a lot of things. Call your friends and family from almost anywhere. Call the police immediately if there is an accident in the street. Send or receive messages. Sending short written messages is a popular way to use your mobile phone. Many people use short forms of words, so the messages are quick to write and read. Can you guess what these messages mean? Try reading them out. What do you hear? RUOK? CUL8r! That's EZ! Will I C U B4 2moro? That's Gr8! | ||
1. The writer talks about _____ uses of a mobile phone. | ||
A. three B. five C. seven D. nine | ||
2. Why did the mobile phones need large powerful batteries some years ago? | ||
A. Because most cities had only one antenna tower. B. Because the mobile phones were too large. C. Because the mobile phones could be used for a long time. D. Because the mobile phones had to send their signal to far-away places. | ||
3. What does the writer think of today's mobile phones? | ||
A. They are small but very powerful. B. They are very popular and cheap. C. They are very easy for us to use. D. They are big enough to send a signal. | ||
4. What does "Will I C U B4 2moro?" probably mean? | ||
A. Will I see you before two past four in the morning? B. Will I see you by 4:02 in the morning? C. Will I see you before tomorrow? D. Will I see you by four tomorrow? | ||
5. What does the writer write the article (文章) for? | ||
A. To give us some common knowledge of the mobile phone. B. To introduce how the mobile phone works and what use it has. C. To tell us what short forms of words mean in written messages. D. To show us in what way the mobile phone is expected to develop. |
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