D

Beyondtwoorthreedays，theworld’sbestweatherforecastsaredoubtful,andbeyondsixorseventheyareworthless.

TheButterflyEffectisthereason.Forsmallpiecesofweather—toaglobalforecaster，smallcanmeanthunder—stormsandblizzards（暴风雪）—anypredictionbecomesworserapidly.Errorsanduncertaintiesincrease，fromdustdevilsandstormsuptocontinent-sizeeddies（旋涡）thatonlysatellitescansee.

Themodernweathermodelsworkwithnet-likepointssixtymilesapart，andevenso，somestartingdatahavetobeguessed，sincegroundstationsandsatellitescannotseeeverywhere.Butsupposetheearthcouldbecoveredwithsensorsplacedonefootapart，risingatone-footintervalsallthewaytothetopoftheatmosphere.Supposeeverysensorgivesperfectlyaccuratereadingsoftemperature，pressure，humidity（温度）,andanyotherdataaweathermanwouldwant.Exactlyatnoonapowerfulcomputertakesallthedataandcalculateswhatwillhappenateachpointat12.01,then12.02，then12.03…thecomputerwillstillbeunabletopredictwhetherPrincetonwillhavesunorrainonemonthaway.Atnoonthespacesbetweenthesensorswillhidefluctuations（波动）thatthecomputerwillnotknowabout.By12.01，thosefluctuationswillalreadyhavecreatedsmallerrorsonefootaway.Soontheerrorswillhaveaddedtotheten-footscale，andsoonuptothesizeoftheglobe.

63．Aweatherforecast____________intheworld.

A．isreliablewithinoneortwodays

B．isdoubtfulbeyond24hours

C．becomesuselessbeyondtwoorthreedays

D．isstillworthwhileinsevendays

64．Usuallythereisaweathersub-station____________.

A．ineverycityB．every60miles

C．betweentwocities　D．everyonefoot

65．Whichofthefollowingstatementsistrue？

A．Peoplehavenotplacedsensorsonefootapartintheatmosphere.

B．Scientistshavealreadyputsensorsonefootapartintheworld.

C．Everysensorgivesperfectlyaccuratedataaweathermanwants.

D．Groundweatherstationsandsatellitescanseeeveryplaceonearth.

66．Ourcomputerwillnotbeabletoknowaboutfluctuationsbecause____________.

A．thesensorsarenotgoodenough

B．theyarehiddenbythespacesbetweenthesensors

C．they