题目内容
（请给出正确答案）
During daylight hours, birds ______.
A．wheel back and forth
B．follow the stars in their flights
C．use sun for guidance
D．are quite likely to get lost
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As you know, the turning of the earth makes the sun and the stars seem to move across the sky. Daylight, of course,【21】, when the sun rises in the east and when the sun is high【22】the sky, between these two positions, half of the daylight hours have been spent.
Therefore, by noticing【23】the sun stood in the sky, early man know they could tell the time of the day, At night the motion of the stars【24】the same purpose. The important thing in keeping time is to know the exact moment of【25】. For each of us, wherever we are, noon is when the sun is directly overhead. Think of an imaginary line【26】the sky, stretching from the north point of your horizon just to the south point.
When the sun cross your meridian (子午线), it is noon for you. When the sun still【27】of this line, or the meridian, it is morning. After the sun has crossed this line, it is【28】.
The Latin word for "midday" is "deridian",【29】which comes our word meridian. So AM is an abbreviation (缩写词) for "ante meridean", or before midday, and PM for after midday. Each or the world's time zones (时区) is about fifteen degrees wide in longitude (经度), which is about the distance the sun moves through tile sky in all hour.【30】lives in the same time zone observes noon at the same moment. In this way, the time is different by one hour as you move through each time zone.
(61)
A．comes
B．begins
C．appears
D．shines
Not long age, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by night？ Tests with artificial stars have proved that certain night - flying birds are able to follow the stars in their long - distance flights.
A dove (鸽子) had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird's cage was placed under an artificial star - filled sky. (76) The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the artificial stars caused a change in the direction of his flight.
(77) But the stars are apparently their principal means of navigation (航行) only. When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it's too dark to see these, the doves circle helplessly, unable to find their way.
The reason why birds don't get lost on long flights ______.
A．have been known to scientists for many years
B．have only recently been discovered
C．are known by us
D．will probably remain a mystery
The findings are based on a German study of almost 700 people who suffered heart attacks. The patients described their activities during the four days before their heart attack. Researchers found that those who had been in traffic were three times more likely to have a heart attack within one hour, compared to those who had not been in traffiC. Most of those in the study had been traveling by car. But some had been on bicycles and others were on buses.
Research shows that people in cars and buses are exposed to ten times the amount of pollutants as people walking on the street. That is largely because they breathe in the particles and gasses released from the vehicles in front of them.
Over time, these small particles speed the buildup of a sticky substance in the blooD. This can cause blockages(阻塞) to form. in the arteries(动脉) around the heart and lead to a heart attack.
Other studies have also linked heart trouble to stress, similar to the kind that people face while driving in heavy traffiC. But the researchers of the latest study say they do not know whether the increased heart attack risk was the result of stress or pollution. They suggest it may be a combination of stress, noise and pollution. Experts say the research shows the need fro cleaner vehicles and better city planning.
9.According to the study, which of the following ways is the safest in traffic？
A. Driving a car
B. Walking on the street
C. Taking a bus
D. Riding a bicycle
9.From among the 700 people who suffered heart attacks we learn that ______.
A. those who have been in traffic are three times as many as those who have not
B. those who have been in traffic for more than one hour are most likely to suffer heart attacks
C. the risk of a heart attack is three higher among those who have been in traffic than those who have not
D. Most of the subjects (实验对象) felt uncomfortable during the four days before the attack
9.The particles released from vehicles ______.
A. build up in the blood
B. become blockages in the arteries
C. make the blood more sticky
D. do harm to the heart
9.According to the studies, which of the following is NOT a likely cause of heart attack？
A. Stress
B. Noise
C. Air pollution
D. Traffic accident
9.What suggestion do experts make to lower the risk？
A. Reducing traffic as much as possible.
B. Living away from nose.
C. Planting more trees in the city.
D. Making vehicles clean.
根据以下内容回答题：
No one knows for sure why birds migrate．One theory of migration says that ancient birds of the northern part of the earth were forced southward during the Ice Age，when ice covered large parts of Europe，Asia and North America．As the ice melted，the birds came back to their homelands，spent the summer，and then went south again in winter．Gradually，these comings and goings became habits，and birds now migrate though much of the ice has gone． Another theory proposes that the ancient home of all modern birds was the tropic areas．There lived so well that the region became overcrowded．Many species had to move northward．During the summer，these birds found plenty of room and food．In winter，however，food be-came scarce and they had to return to the south． A newer theory is that increasing daylight stimulates certain glands（腺）in the bird’s body and prepares it for migration．One scientist is able to make birds migrate in midwinter by expo-sing them for two months to artificial daylight．Recoveries of marked birds indicate that they fly north as soon as they are set free．The conclusion is that the urge to migrate is determined by changes in the bird’s body which take place under seasonal changes in the length of daylight． This theory would account for the fact that not all birds migrate at the same time．Each sDecies seems to have its own schedule．The theory would also account for the regular time and rou‘tes of migration．Birds arrive at a given place year after year．Unfavorable weather delays them only a few days．Total hours of daylight，rather than weather，start them on the way． How birds find their way to the same place year after year and why they follow their own Darticular route are still mysteries．They evidently do not follow known landmarks，for many young birds migrate alone without the help of experienced adults．
We can conclude from the first paragraph that__________ ．
A.during the Ice Age，the whole Europe was covered with ice
B.the south used to be the homelands of all birds
C.scientists can confidently explain why birds migrate now
D.migration of birds can be explained by the change of ice on earth
