ReadthefollowingpassageandmarktheletterA,B, C,orD onyouranswersheettoindicatethecorrectanswertoeachofthe questions.

Quitedifferentfromstormsurgesarethegiantseawavescalledtsunamis, whichderivetheirnamefromtheJapaneseexpressionfor“highwaterina harbor.”Thesewavesarealsoreferredtobythegeneralpublicastidalwaves, althoughtheyhaverelativelylittletodowithtides.Scientistsoftenreferredto themasseismicseawaves,farmoreappropriateinthattheydoresultfrom underseaseismicactivity.Tsunamisarecausedwhentheseabottomsuddenly moves,duringanunderwaterearthquakeorvolcanoforexample,andthewater abovethemovingearthissuddenlydisplaced.Thissuddenshiftofwatersets off a series of waves. Thesewaves can travel great distances at speeds closeto 700kilometersperhour.Intheopenocean,tsunamishavelittlenoticeable amplitude,oftennomorethanoneortwometers.Itiswhentheyhittheshallow watersnearthecoastthattheyincreaseinheight,possiblyupto40meters. TsunamisoftenoccurinthePacificbecausethePacificisanareaofheavy seismicactivity.TwoareasofthePacificwellaccustomedtothethreatof tsunamisareJapanandHawaii.Becausetheseismicactivitythatcauses tsunamisinJapanoftenoccursontheoceanbottomquiteclosetotheislands, thetsunamisthathitJapanoftencomewithlittlewarningandcan,therefore, prove disastrous. Mostofthe tsunamisthathit the HawaiianIslands, however, originatethousandsofmilesawaynearthecoastofAlaska,sothesetsunamis haveamuchgreaterdistancetotravelandtheinhabitantsofHawaiigenerally havetimeforwarningoftheirimminentarrival.Tsunamisarecertainlynot limitedtoJapanandHawaii.In1755,Europeexperiencedacalamitous tsunami,whenmovementalongthefaultlinesneartheAzorescausedamassive tsunamitosweepontothePortuguesecoastandfloodtheheavilypopulated areaaroundLisbon.Thegreatesttsunamionrecordoccurredontheotherside oftheworldin1883whentheKrakatoavolcanounderwentamassive explosion,sendingwavesmorethan30metershighontonearbyIndonesian islands;thetsunamifromthisvolcanoactuallytraveledaroundtheworldand was witnessed as far away as the EnglishChannel.

“It” in the passage refers to_______.