Someradiosingalswereheardin1967.Theywerecomingfromapointintheskywheretherewasunknownstar.Theywerecomingveryregularly,too:aboutonceasecond,iftheywerecontrolledbyclock.
Thescientistswhoheardthesignalsdidnottellanybodyelse.Theywereratherafraidtotellincasetheyfrightenedpeople.Thesignalswerecomingfromaverysmallbody—nobigger,perhapsthantheearth.Wasthatwhynolightcouldbeseenfromit?Orwerethesignalscomingfromaplanetthatbelongedtosomeotherstar?Therewasnoendtothequestions,butthescientistskeptthenewssecret.“Perhapsthereareintelligentbeingsoutthere.”theythought,“whoaretryingtosendmessagestootherplanets,ortous?Sothenewswasnotgiventothenewspaper.Instead,thescientistsstudiedthesignalsandsearchedforotherslikethem...Well,allthathappenedin1967and1968.Sincethenscientistshavelearntmoreaboutthosestrange,regular,radiosignals.Andtheyhavetoldthestory,ofcourse.
Thesignalsdonotcomefromaplanet;theycomefromanewkindofstarcalleda“pulsar””.Aboutahundredotherpulsarshavenowbeenfound,andmostofthemareverylikethefirstone.
Pulsarsarestrongradiostars.Theyarethesmallestbuttheheavieststarsweknowatpresent.Ahandfulofpulsarwouldweighafewthousandtons.Theirlight—iftheygivemuchlight—istoosmallforustosee.Butwecanbesureofthis,nointelligentbeingsarelivingonthem.
21.Theradiosignalsdiscussedinthispassage____.
A.wereregularB.werecontrolledbyaclock
C.wereheardin1967onlyD.weresecretmessages
22.Theradiosingalsweresentby____.
C.askybodywhichwasunknownatthattime
D.intelligentbeingswhowereunknownatthattime
23.Thescientistsdidnottellpeopleaboutthesignalsbecause____.
A.thesingalsstoodforsecretmessages
B.peoplewouldaskthemtoomanyquestions
C.theydidnotwanttofrightenpeople
D.theystoodforunimportantmessages
24.Apulsaris____.
A.asmallheavystarwhichsendsoutstrongradiosignalsandcannotbeseen
B.asmallheavyplanetwhichsendsoutstrongradiosignalsandcannotbeseen
C.asmallheavysatellitewhichsendsoutstrongradiosignalsandcannotbeseen
D.asmallintelligentbeingwhosendsoutstrongradiosignalsandcannotbeseen
25.Whichofthefollowingistrue?
A.Oneofthepulsarsfoundbyscientistssendsradiosignals.
B.Pulsarbegantosendradiosingalsin1967.
C.Scientistshavesearchedforpulsarsformanyyearsbutfoundnone.
D.Scientistshavefoundmanypulsarssince1967.
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