阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项。Housesfalldown.Treesfallover.Largeholesformintheground.CouldAlaskabesinking?That’swhatsomevillagersinAlaskahavebeenaskingthemselvesrecentlyandscientiststhinktheyknowwhy.WarmertemperaturesmaybecausingAlaska’sfrozengroundtothaw(解冻).About85percentofAlaska’slandsurfacehaspermafrost(永久冻结带).Permafrostsupportsthegroundaboveit—includingtrees,houses,androads.Butwhyisthepermafrostthawing?Somescientistssaythathuman-causedpollutionisleadingtoglobalwarming.AndmostscientistsagreethatAlaskahasbeengettingwarmer.Theysaythatthewarmertemperatureiscausingpermafrosttothawinsomeareas.Thethawingpermafrostcancauseproblemsforpeople,plants,andanimals.Thecollapsing(倒塌)isaprobleminthevillagesinAlaskawhicharebuiltonpermafrost,andsomeofthemmayhavetomovetosaferground,wherethereisnopermafrost.TheAlaskantownofGlennallensawitsoldpostofficecollapse.And,accordingtoJamesWalters,apermafrostexpertattheUniversityofNorthernIowa,house-movingcompanieshavebeenverybusy.“Meltingpermafrostcanalsodestroytreesandforests,”Walterssaid.“Whenholesinthegroundform,treesfallintothemanddie.Thiscouldturnaforestintoaswamp(沼泽),andanimalswhichneedtheforestswillhavetomoveelsewhere.”“Themeltingcouldcausesevereproblems.”Walterssays,“Thiscouldtakehundredsofyears,butintheendAlaskawilllookquitedifferentfromwhatitlookslikenow.”1.Whichofthefollowingcanbeusedasthebesttitleofthepassage?A.Alaska—AFrozenLandB.IsAlaskaSinking?C.PollutionandGlobalWarmingD.AlaskaIsPolluted2.Themainreasonwhypermafrostisthawingisthat______.A.thetemperatureinAlaskaisrisingB.peopleinAlaskadon’ttakecareofpermafrostC.toomanyhousesarebuiltonpermafrostD.peopleinAlaskapollutedpermafrost3.ThefollowingaretheresultsofmeltingpermafrostEXCEPT______.A.holesforminthegroundB.aforestwillbeturnedintoaswampC.someanimalshavetogoelsewhereD.morewaterwillbeneededbypeopleandanimals4.WhichofthefollowingisNOTtrueaccordingtothepassage?A.Whenpermafrostmelts,houseswillfalldown.B.House-movingcompaniesarebusybecausetheirhousesa