ReadthefollowingpassageandmarktheletterA,B,C,orD onyouranswersheettoindicatethecorrectanswertoeachofthe questions.

Centuriesago,mandiscoveredthatremovingmoisturefromfoodhelpedto preserveit,andthattheeasiestwaytodothiswastoexposethefoodtosunand wind.InthiswaytheNorthAmericanIndiansproducedpemmican(driedmeat groundintopowderandmadeintocakes),theScandinaviansmadestockfish and the Arabs dried dates andapricots.

Allfoodscontainwater-cabbageandotherleafvegetablescontainasmuch as93%water,potatoesandotherrootvegetables80%,lean meat75%andfish anythingfrom80%to60%dependingonhowfattyitis.Ifthiswateris removed, the activity of the bacteria whichcause food to go bad is checked.

Fruitissun-driedinAsiaMinor,Greece,SpainandotherMediterranean countries,andalsoinCalifornia,SouthAfricaandAustralia.Themethodsused vary,butingeneralthefruitisspreadoutontraysindryingyardsinthehot sun.Inordertopreventdarkening,pears,peachesandapricotsareexposedto thefumesofburningsulphurbeforedrying.Plumsformakingprunes,and certainvarietiesofgrapesformakingraisinsandcurrants,aredippedinan alkalinesolutioninordertocracktheskinsofthefruitslightlyandremovetheir wax coating, so increasingthe rate of drying.

Nowadaysmostfoodsaredriedmechanically;theconventionalmethodof suchdehydrationistoputfoodinchambersthroughwhichhotairisblownat temperaturesofabout110oCatentrytoabout45oCatexit.Thisistheusual method for drying such things as vegetables, mincedmeat, and fish.

Liquidssuchasmilk,coffee,tea,soupsandeggsmaybedriedbypouring themoveraheatedhorizontalsteelcylinderorbysprayingthemintoachamber through which a current of hot air passes. In the first case, the dried material is scrapedofftherollerasathinfilmwhichisthenbrokenupintosmall,though stillrelativelycoarseflakes.Inthesecondprocessitfallstothebottomofthe chamberasafinepowder.Whererecognizablepiecesofmeatandvegetables are required, as in soup, the ingredients are dried separately and then mixed.

Driedfoodstakeuplessroomandweighlessthanthesamefoodpackedin cansorfrozen,andtheydonotneedtobestoredinspecialconditions.Forthese reasonstheyareinvaluabletoclimbers,explorersandsoldiersinbattle,who havelittlestoragespace.Theyarealsopopularwithhousewivesbecauseit takes so little time to cook them.

What is the main idea of the passage?