PassageTwoBecausehelicopterscangoalmostanywhere,theyhavebeenespeciallyusefultoexplorers.InthejunglesofSouthAmericatheyhavehelpedexplorerslookingfornewplacestosinkoilwells.Firstofallthehelicoptersliftthegeologistsandmineralogists（矿物学家）intotheheartofjungle,tryingfirstoneareaandthenanother,andwhentheyfindaplacethatseemslikelytoyieldoil,thehelicoptercanbringindrillingequipment.Theycanbringinhutsinpieces,andverynearlyeverythingthatmaybeneeded.Ifatelephoneisneededfromthejungleoutpost（前哨）backtothemainbase,thenthewiresthemselvescanbelaidacrossthejungletreetops.Allthehelicopterhastodoistoflycloseoverthetreesunreelingthecablefromadrumasitgoes.Itisverycomfortingforexplorersinsuchplacestoknowthatiftheyareinjuredorfallill,theycanbeflownbacktohospitalinafewhours.Onlytwentyyearsagoasickmanprospectingintheheartofthejunglemighthavefacedajourneyofseveralweeks,travelingpartofthewayonabumpingstretcher（担架）carriedbynatives,andpartofthewayinaslow-movingcanoe.Bighelicopterscanliftloadsuptoabouttentons.Astheycangoeverywhereandcanhoveroveranychosenspot,thesehelicoptersmakeexcellentflyingcranes.Beforethedaysofhelicopters,thetaskofbuildingaradiostationontopofahighmountainmighthavemeantbuildingaroadoracablerailwayfirst.Butahelicoptercancarryallthebuildingmaterialsandtheworkmenupintothepositionquiteeasily.Puttinganewtoponahighstructurelikealighthouseusedtomeanthatascaffolding（脚手架）evenhigherthanthelighthousehadtobebuiltfirstofall.Nowahelicoptercanbeusedtoflyoverandlowerthepartgentlyintoposition.Ahelicopterhasbeenusedtolowernewcrossontothespireofachurchinthesameway.Helicoptershavesavedthousandsofpeoplefromtheseaandtheyhavesavedpeoplefrommountaintops.Theyarealreadydoingallkindsofusefulthingsbuttheirstoryhashardlybegun.6.Thehelicopternowcanhelpusdomanythings,whichofthefollowingisnotmentionedbytheauthor?A.Itcanhelppeoplebuildnewbridges.B.Itcansavepeoplefrommountains.C.Itcanloweranewcrossontoaspireofachurch.D.Itcanputanewtoponahighbuilding.7.Whatdoes“they”(Para.1Line4)referto?A.Helicopte