词汇与问答题.docx

词汇与问答题.docx

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词汇与问答题

SectionB（9分）

Directions:

Completethepassagebyusingtheproperwordsinthebox．Eachwordcanonlybeusedonce．Notethatthereisextrawordinthebox．

A．valuableB．involvedC．motivatedD．contribute

E．convenientF．servicesG．generousH．efforts

I．rewardsJ．contact

Communitiesalwayshaveneedsthataredifficulttomeet．Volunteers,offeringtheir____1_____forfree,canbeabighelp．Throughtheirunselfish__2____,theymakecaringforothersanimportantpartoflife．

Volunteersare___3____byavarietyofthings,butallofthemagreethatthe___4___ofcharitableworkcanbeprecious．Itiseasytomeetpeoplewithsimilarinterests,whichisimportanttomostvolunteers．Voluntaryworkisalsoa__5____wayforteenagerstodevelopnewskillsandgain____6_____experience,aswellasmakeusefulcontacts．Thiscanleadtoemploymentopportunitiesinthefuture．

Itisverysimpleifyouwanttoget____7___.Startbymakingsomeenquiriesatschool．Yourteacherwillbeabletogiveyouplentyofadviceonwhomto__8_____ifyouwantto__9____someofyourtimetoavoluntaryorganization．

1-9FHCIEABJD

TheEarthhasaforcethatpullsthingstowarditself．Wecallthisforcegravity．Thisissomethingwelivewithallthetime,andhardlyeverthinkaboutit．Butitisamostimportantfactorinrocketoperationandmustbeovercomeifwearetogetanywhereinspace,oroffthegroundatall．

Takethethrowingofaballasanexample．Thehardertheballisthrown,thefasterandhigheritwillgo．Whatisthesecret?

Itsspeed．Ifwecouldthrowtheballhardenoughitwouldgoupandupforeverandnevercomedown．Thespeedatwhichitwouldhavetobethrowntodothisisknownasescapespeed．Ofcourse,wecannotthrowaballhardenoughbecausethespeed,requiredtoescapecompletelyfromtheEarth'sgravityissevenmilespersecond,orovertwenty-fivethousandmilesperhour．

Onceescapespeedhasbeenreachedbyaspaceship,nofurtherpowerisneeded．ArocketaimedattheMoon,forinstance,will"coast"therestofthewaybecausetheEarth'sgravitycannotthenpullitback,andthereisnoairresistanceinspacetoslowitdown．This"coasting"isknownas"freefall"．ThatdoesnotmeantherocketisfallingdowntowardstheEarthbutthatitistravelingfreelyinspacewithoutthehelpofpower,likeabicyclecoastingdownhill．

Freefallisanimportantfeatureofspacetravel：

itwouldbeimpossibletocarryenoughoiltosupplypoweredflightallthetime．

1．HowfastwillarocketescapecompletelyfromtheEarth'sgravity?

2．AsthereisalwaystheEarth'sgravitationalpull,people．

3．Whenabicycle"coasts"downhill,it．

4．Whyisitunnecessarytosupplypowerfortheflightinspaceallthetime?

1．Sevenmilespersecond．/Twenty-fivethousandmilesperhour．

2．hardlyeverthinkaboutit．/acceptitwithoutquestioningit．

3．doesnotneedanyfurtherpower．

4．Becausenofurtherpowerisneededaftertheescapespeedisreached