阅读理解Itissaidthatalldreamsserveapurpose(目的).Whilethereisnoagreementamongscientistsaboutwhywedream,therearemanyideasaboutthedifferentkindsofdreamswehave.Onecommonkindofdreamistherepeatingdream,inwhichthesamestoryisrepeatedagainandagain,oftenformanymonthsorevenyears.Somebelievetheseareasignpeoplehaveaproblemintheirlifeandoncethatproblemisgonethenthedreamwillstop.Othersthinktheyareawaytohelppeopleremembersomethingveryimportant.Anotherwell-knownkindofdreamisthenightmare.Thepicturesandstoriesinsuchdreamsmakepeopleveryafraidanddreamersusuallyrememberthemfarmoreclearlythannormaldreams.Thecauseofsuchdreamsmaybeseeingsomethingterrifyingsuchasacaraccidentorsomedeadlysnakes.Othersthinksuchdreamsmaybetryingtomakeapersonpayattentiontosomethingthatisdangerousintheirlife.Daydreamshappenduringwake-timewhenweforgetwhereweareorwhatwearedoingandfindourselvesinamade-upstoryorunrealworld.Weoftendaydreamwhenwearedoingsomethingthatisnotinterestingorexciting.Theyhelpusthinkaboutourfuture.Luciddreamsarethemostfun.Thesehappenwhendreamerssuddenlyunderstandthattheyaredreaming.Insteadofwakingup,theystayinthedreamandareabletocontrolwhathappensinthedreamasiftheyaremakingamovie.小题1:Theunderlinedword“they”(inparagraph2)refersto“_________”.