Radar is an example of acronym.（)

Space-Age Archeology

It's a strange partnership, but a very effective one: Satellites and space-shuttle-carried radar are helping archeologists. How？ By "seeing" through sand or through treetops to locate important archeological sites.

The traditional tools of archeologists are shovels and picks. But high technology is making the archeologist's work and time far more productive.

Take, for example, the second 1981 flight of the Space Shuttle Challenger. During that mission, a powerful, experimental radar was pointed at a lifeless stretch of desert in Egypt called the Selima Sand Sheet (part of the Sahara Desert). To everyone's surprise, the radar penetrated through the sand to the harder rock beneath. On the surface, there is a little indication that Africa's Sahara Desert was never anything but a desert. When the archeologists studied the radar images, they saw what seemed to be impossible: there was sand-buried landscape. that was shaped by flowing water; traces of ancient riverbeds appeared to be over nine miles wide, far wider than most sections of the present-day Nile River. Today, the area is one of the hottest, driest desert in the world.

Archeologists dug pits along the old river banks and found clues to the past: stream-rounded pebbles (鹅卵石), Stone-Age axes, broken ostrich (鸵鸟) eggshells, and the shells of land snails. The archeologists were quite pleased with these findings. For years, they'd been finding stone axes scattered through, the-desert, and couldn't understand why. Now we know that early humans were living on the banks of old rivers, and left their beautiful tools behind. Some are so sharp that you could shave with them.

More recently, Landsat 4, a special Earth-mapping satellite, aided in the discovery of ancient Mayan ruins in Mexico. Landsat can, with the help of false-color imagery, "see through" much of the area. Armed with these maps, a five-person expedition took to the air in a helicopter.

By the end of the second day, the team found a stretch of walled fields that expedition members said look like "old New England fences". They just go on, non-stop, for 40 miles. Later in the week, an ancient village was pinpointed, as was the "lost" city of Oxpemul, once found in the early 1930's but quickly reclaimed by the jungle. The findings made them able to map the extent of the Mayan civilization in about five days. Working on foot, it would, have taken at least 100 years.

With the help of the space-shuttle-carried radar, archeologists found

A．a new stretch of the Sahara desert.

B．traces of ancient riverbeds under the Sahara Desert.

C．some traditional archeological tools in the Sahara Desert.

D．a mountain beneath the Sahara Desert.

Space-Age Archeology

It's a strange partnership, but a very effective one: Satellites and space-shuttle-carried radar are helping archeologists. How？ By "seeing" through sand or through treetops to locate important archeological sites.

The traditional tools for archeologists are shovels and picks. But high technology is making the archeologist's work and time far more productive.

Take for example, the second 1981 flight of the Space Shuttle Challenger. During the mission, a powerful, experimental radar was pointed at a lifeless stretch of desert in Egypt called the Selima Sand Sheet(part of the Sahara Desert). To everyone's surprise, the radar penetrated through the sand to the harder rock beneath. On the surface, there is a little indication that Africa's Sahara Desert was never anything but a desert. When the archeologists studied the radar images, they saw what seemed to be impossible: there was sand-buried landscape that was shaped by flowing water; traces of ancient riverbeds appeared to be over nine miles wide, far wider than most sections of the present-day Nile River. Today, the area is one of the hottest, driest desert in the world.

Archeologists dug pits along the old river banks and found clues to the past: stream-rounded pebbles (鹅卵石), Stone-Age axes, broken ostrich (鸵鸟) eggshells, and the shells of land snails. The archeologists were quite pleased with these findings. For years, they'd been finding stone axes scattered through the desert, and couldn't understand why. Now we know that early humans were living on the banks of old rivers, and left their beautiful tools behind. Some are so sharp that you could shave with them.

More recently, Landsat 4, a special earth-mapping satellite, aided in the discovery of ancient Mayan ruins in Mexico. Lansat can, with the help of false-color imagery, "see through" much of the area. Armed with these maps, a five-person expedition took to the air in a helicopter.

By the end of the second day, the team found a stretch of walled fields that expedition members said look like "old New England fences". They just go on, non-stop, for 40 miles. Later in the week, an ancient village was pinpointed, as was the "lost" city of Oxpemul, once found in the early 1930's but quickly reclaimed by the jungle. The findings made them able to map the extent of the Mayan civilization in about five days. Working on foot, it would have taken at least 100 years.

With the help of the space-shuttle carried radar, archeologists found ______.

A．a new stretch of the Sahara desert

B．traces of ancient riverbeds under the Sahara Desert

C．some traditional archeological tools in the Sahara Desert

D．a mountain beneath the Sahara Desert

and severe thunderstorms, begin quickly, strike suddenly, and disappear rapidly, destroying small regions while leaving neighboring areas untouched. Conventional (普通) computer models of the atmosphere have limited value in predicting short-lived local storms because the available weather data are generally not detailed enough to allow computers to see clearly the small atmospheric changes that come before these storms. In most nations, for example, weather-balloon observations are taken just once every twelve hours at location typically separated by hundreds of miles. With such limited data, conventional forecasting models do a much better job predicting general weather conditions over large regions than they do forecasting specific local events.

Until recently, the observation-intensive approach needed for accurate, very short range forecasts, or "nowcasts" , was impracticable. The cost of equipping and operating many thousands of conventional weather stations was extremely high, and the difficulties involved in rapidly collecting and processing the raw weather data from such a network were beyond overcoming. Fortunately, scientific and technological advance have overcome most of these problems. Radar systems, automated weather instruments , and satellites are all capable of making detailed, nearly continuous observations over large regions at a relatively low cost. Communication satellites can transmit data around the world cheaply and immediately, and modern computers can quickly compile and analyze this large volume of weather information. Meteorologists (气象学家) and computer scientists now work together to design computer programs and video equipment capable of transforming raw weather data into words, symbols, and vivid graphic displays that forecasters can interpret easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, nowcasting is becoming a reality.

What is the best title of the passage？

A．Severe Thunderstorms and Damages

B．Weather Forecasting and Life-threatening

C．Science Advances and Nowcasts

D．Available Data and Nowcasts

Implied but not stated ______ .

A．Laser-dopple radar is more accurate than microwave radar

B．Microwave radar may not ensure absolute precision in measuring varying speeds

C．The light-beam radar can measure only slow speeds with accuracy

D．Microwave radar operates at a higher frequency than laser-dopple radar

Questions are based on the following passage.

Many of the most damaging and life threatening types of weather, such as torrential rains and severe thunderstorms, begin quickly, strike suddenly, and disappear rapidly, destroying small regions while leaving neighboring areas untoucheD．(79) Conventional (普通) computer models of the atmosphere have limited value in predicting short-lived local storms because the available weather data are generally not detailed enough to allow computers to see clearly the small atmospheric changes that come before these storms. In most nations, for example, weather-balloon observations are taken just once every twelve hours at location typically separated by hundreds of miles. With such limited data, conventional forecasting models do a much better job predicting general weather conditions over large regions than they do forecasting specific local events.

Until recently, the observation-intensive approach needed for accurate, very short range forecasts, or "nowcasts", was impracticable. The cost of equipping and operating many thousands of conventional weather stations was extremely high, and the difficulties involved in rapidly collecting and processing the raw weather data from such a network were beyond overcoming. Fortunately, scientific and technological advance have overcome most of these problems. Radar systems, automated weather instruments, and satellites are all capable of making detailed, nearly continuous observations over large regions at a relatively low cost. Communication satellites can transmit data around the world cheaply and immediately, and modem computers can quickly compile and analyze this large volume of weather information. (80) Meteorologists (气象学家) and computer scientists now work together to design computer programs and video equipment capable of transforming raw weather data into words, symbols, and vivid graphic displays that forecasters can interpret easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, nowcasting is becoming a reality.

What is the best title of the passage？ 查看材料

A.Severe Thunderstorms and Damages

B.Weather Forecasting and Life-threatening

C.Science Advances and Nowcasts

D.Available Data and Nowcasts

ce ________ ？

A.used

B.available

C.in use

D.can be used

Implied but not stated is that__________．

A.laser—doppler radar ismore accurate than microwave radar

B.microwave radar operatesat a higher frequency than laser—doppler radar

C.the light—beam radar canmeasure only slow speeds with accuracy

D.microwave radar may notensure absolute precision in measuring varying speeds

thunderstorms, and tornadoes--begin quickly, strike suddenly, and dissipate rapidly, devastating small regions while leaving neighboring areas untouched. One such event, a tornado, struck the northeastern section of Edmonton, Alberta, in July 1987. Total damages from the tornado exceeded ＄ 250 million, the highest ever for any Canadian storm. Conventional computer models of the atmosphere have limited value in predicting short-lived local storms like the Edmonton tornado, because the available weather data are generally not detailed enough to allow computers to discern the subtle atmospheric changes that precede these storms. In most nations, for example, weather-balloon observations are taken just once every twelve hours at locations typically separated by hundreds of miles. With such limited data, conventional forecasting models do a much better job predicting general weather conditions over larger regions than they do forecasting specific local events.

Until recently, the observation--intensive approach needed for accurate, very short-range forecasts, or "Nowcasts", was not feasible. The cost of equipping and operating many thousands of conventional weather stations was prohibitively high, and the difficulties involved in rapidly collecting and processing the raw weather data from such a network were insurmountable. Fortunately, scientific and technological advances have overcome most of these problems. Radar systems, automated weather instruments, and satellites are all capable of making detailed, nearly continuous observation over large regions at a relatively low cost. Communications satellites can transmit data around the world cheaply and instantaneously, and modern computers can quickly compile and analyzing this large volume of weather information. Meteorologists and computer scientists now work together to design computer programs and video equipment capable of transforming raw weather data into words, symbols, and vivid graphic displays that forecasters can interpret easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, Nowcasting is becoming a reality.

What does the passage mainly discuss？

A．Computers and weather.

B．Dangerous storms.

C．Weather forecasting.

D．Satellites.

to cede control to the powers that be, becoming at one with the universe as they breathe in the mind-numbing fumes all around. At worst, it is an on-going battle for sanity. But now, according to several groups of researchers in America and Germany, there is something that drivers can do to take back control over the roads. Get adaptive cruise control. And, of course, use it.

Adaptive cruise control (ACC) , as its name suggests, is a modified version of traditional cruise control. It employs radar to monitor the road ahead of a vehicle, automatically adjusting that vehicle' s speed to maintain a safe distance from the one in front. This is safer than manual driving because it reduces the system' s reaction time from nearly a second (human) to practically instantaneous (machine) , thus helping to forestall shunts. But ACC may have a useful side-effect, arising from the fact that another effect of slow human reaction times is to produce traffic jams on apparently open roads.

Such jams start when a car slows suddenly to allow, for example, another vehicle to enter the traffic stream. Slow reaction times mean that instead of responding smoothly, the drivers behind such a vehicle often end up slamming on the brakes. That skimming propagates backwards, and before long (he traffic is at a standstill. So it makes sense that ACC would reduce not only collisions, but also congestion. What is unexpected is how few vehicles need to have it operating for all to benefit. As Craig Davis of the University of Michigan reports in Physical Review E, only 20% of cars need to employ ACC in order to present completely those jams that are caused by a slow lead car on a high-speed, single-lane road. According to Dr. Davis' s computer model, even a rate of use of ACC as low as 13% can improve the flow of traffic significantly.

ACC is not a panacea. Dr. Davis got less promising results for more complex, road conditions, particularly those near junctions. And a .similar model built by Boris Kernel', a researcher for Daimler Chrysler, in Stuttgart, Germany, indicates that in certain bottleneck conditions, ACC may even cause extra congestion. These disappointing results can, however, be ameliorated by shortening the "headway" in ACC-equipped vehicles, according to Martin. Treiber of the Dresden University of Technology', also in Germany.

Headway is the gap, measured in seconds, that a driver puts between himself and the car ahead. Since ACC reacts more quickly than a human, people who have it fitted can afford to allow less headway.

Summary :

Stationary traffic can drive people mad. However, according to American and German researchers, adaptive cruise control (ACC) can help drivers take【71】. ACC adapts a car's speed to keep a sale distance from the one ahead by using radar to monitor the road ahead. ACC is safer than manual driving because is significantly reduces the system's【72】, and collisions and congestion in addition. According to Dr. Davis' computer model, if【73】of cars use ACC, the flow of traffic can be improved significantly. However, ACC should not be seen as a panacea. In【74】conditions, it may even cause extra jams, according to a computer model. But this situation can be improved by reducing【75】in ACC-equipped vehicles.

(30)