Many of the most damaging and life-threatening types of weather - torrential rains， severe thunderstorms， and tornadoes - begin quickly， strike suddenly， and dissipate rapidly，devastating small regions while leaving neighboring areas untouched. One such event， a tornado， stuck 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 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 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.

　　30.What does he passage mainly discuss？

　　（A） Computers and weather

　　（B） Dangerous storms

　　（C） Weather forecasting

　　（D） Satellites

　　31.Why does the author mention the tornado in Edmonton， Canada？

　　（A） To indicate that tornadoes are common in the summer

　　（B） To give an example of a damaging storm

　　（C） To explain different types of weather

　　（D） To show that tornadoes occur frequently in Canada

　　32.The word "subtle" in line 8 is closest in meaning to

　　（A） complex

　　（B） regular

　　（C） imagined

　　（D） slight

　　33.Why does the author state in line 10 that observations are taken "just once every twelve hours？"

　　（A） To indicate that the observations are timely

　　（B） To show why the observations are on limited value

　　（C） To compare data from balloons and computers

　　（D） To give an example of international cooperation

　　34.The word "they" in line 13 refers to

　　（A） models

　　（B） conditions

　　（C） regions

　　（D） events

　　35.Which of the following is NOT mentioned as an advance in short - range weather forecasting？

　　（A） Weather balloons

　　（B） Radar systems

　　（C） Automated instruments

　　（D） Satellites

　　36.The word "compile" in line 23 is closest in meaning to

　　（A） put together

　　（B） look up

　　（C） pile high

　　（D） work over

　　37.With Nowcasting， it first became possible to provide information about

　　（A） short-lived local storms

　　（B） radar networks

　　（C） long - range weather forecasts

　　（D） general weather conditions

　　38.The word "raw" in line 25 is closest in meaning to

　　（A） stormy

　　（B） inaccurate

　　（C） uncooked

　　（D） unprocessed

　　39.With which of the following statements is the author most likely to agree？

　　（A） Communications satellites can predict severe weather.

　　（B） Meteorologists should standardize computer programs.

　　（C） The observation - intensive approach is no longer useful.

　　（D） Weather predictions are becoming more accurate.

　　40.Which of the following would best illustrate Nowcasting？

　　（A） A five-day forecast

　　（B） A warning about a severe thunderstorm on the radio

　　（C） The average rainfall for each month

　　（D） A list of temperatures in major cities