Therocketengine, withitssteadyroarlikethatofawaterfallorathunderstorm, isanimpressivesymbolofthenewspaceage.Rocketengineshave 1 powerfulenoughtoshootastronauts 2 theearthsgravitationalpulland 3 themonthemoon.Wehavenowbecome 4 space.
Impressiveandcomplex 5 itmayappear, therocket, whichwas 6 inChinaover 800 years 7 , isarelativelysimpledevice.Fuelthatis 8 intherocketenginechanges 9 gas.Thehotandrapidly 10 gasmustescape, butitcandosoonly 11 anopeningthat 12 backward.Asthegasis 13 withgreatforce, it 14 therocketinthe 15 direction.Likethekickofagun 16 itisfired, it 17 thelawsofnature 18 bySirIsaacNewtonwhenhediscoveredthat 19 everyaction, thereis 20 equalandoppositereaction.
1.A.shownB.beenC.appearedD.proved
2.A.againstB.despiteC.beyondD.from
3.A.sendB.landC.takeD.carry
4.A.travelersB.astronautsC.researchersD.explorers
5.A.thatB.soC.asD.sometime
6.A.madeB.discoveredC.developedD.invented
7.A.inadvanceB.beforeC.earlierD.ago
8.A.roundB.containedC.storedD.burned
9.A.asB.intoC.forD.the
10.A.heatingB.escapingC.expandingD.conducting
11.A.inB.atC.byD.through
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