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【单选题】As spring unfolds across NorthAmerica, tornadoes once again are in the news. It’s a reminder that the United States is the severe-storm capital of the worlD、
Describing this status recently in theBulletin of theAmerican Meteorological Society,Elbert W. Friday Jr., National Weather Service director, observed that "the United States experiences more severe local storms and flooding than any other country in the worlD、" He added that a typical year brings "some 10000 violent thunderstorms, 5000 floods, and 1000 tornadoes. "
Yet the country is not helpless before this onslaught, thanks to advances in meteorological knowledge and in the forecast and warning system, the tornado death rate, for example, has been cut in half in recent decades. It’s down from nearly 2000 per decade 60 years ago to less than 1000 per decade today.
Now the weather service is poised for what Mr. Friday calls "a meteorological revolution. " Sharp-eyed new radars, more vigilant weather satellites, and computerized-information handling will bring what he calls "dramatic improvements in... forecasts anD、., detection of and warnings for severe weather. " This is particularly true for tornadoes.
These funnel-shaped circulations develop in association with severe thunderstorms.As the NationalCenter forAtmospheric Research (NCAR) inBoulder,Colo., explains, the funnels often form at the thundercloud base.But tornado spotters also have to watch what’s happening on the grounD、The first clue may be swirling dust and debris.
Of the 710 to 1000 tornadoes reported annually in the US, about 79 percent are what theAmerican Meteorological Society calls " weak ".About 20 percent are "strong"About 1 percent are "violent".
Weak funnels last under 10 minutes and have wind speeds on the order of 110 miles per hour. They leave ground tracks less than a mile long and 100 yards wide.Although called "week", they are potentially dangerous, while their short lifetimes make timely warnings difficult.
Strong tornadoes last from 10 minutes to more than two hours. Maximum winds, as estimated from damage surveys, range up to 280 mph or higher.
A、single thunderstorm cell may produce these powerful tornadoes in cycles.Each such sequence may last for tens of minutes. It can leave damage trails over 100 miles long by 1000 yards wide.
Tornadoes have touched towns throughout NorthAmerica in every month of the year.But NCAR notes that they occur predominantly over the Great Plains and Midwest and are common inEaster states and the Gulf of Mexico. Their region of most frequent occurrence begins near the GulfCoast in March and shifts toward Kansas, Iowa, and Nebraska by May and June.

A、weather satellite LaunchedApril 13 will help forecasters monitor this tornado "season". The $220 million GOES-8 (Geostationary OperationalEnvironmental Satellite), the first of five improved weather "eye", can pinpoint storms to within 1.2 miles, compared with 6.2 to 12.4 miles for the old system.

A、new class of radars is also part of the meteorological "revolution". Unlike their predecessors, they sense motion of clouds, rain, and wind-borne debris. There will be 150 such radar sites. The National Weather Service will have 121. The FederalAviationAgency and theDepartment ofDefense will operate the other installations and share data with the Weather Service.
According to Paragraph 4, the U. S. Weather Service is ______.

A、reluctant to change
B、on the brink of change
C、inefficient and outdated
D、already technologically advanced
网考网参考答案：B
网考网解析：
这段第一句话说到美国气象服务中心已经准备好“气象革命”。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>