Millionsofpeoplearoundtheworldcooktheirfoodoversmokyfireeveryday.Itisoftendifficulttofindwoodforthefire.Peoplewhodonothavewoodmustspendlargeamountsofmoneyoncookingfuel.Howeverthereisamucheasierwaytocookfoodusingenergyfromthesun.
Solarcookerorovenshavebeenusedforcenturies.ASwissscientistmadethefirstsolaroveninseventeensixty-seven.Todaypeopleareusingsolarcookersinmanycountriesaroundtheworld.Peopleusesolarovenstocookfoodandtoheatdrinkingwatertokillbacteriaandotherharmfulorganisms.
Therearethreekindsofsolarovens.ThefirstisaboxcookerItisdesignedwithaspecialwallthatshinesorreflectssunlightintothebox.Heatgetstrappedunderapieceofglassorplasticcoveringthetopofthecooker.Aboxoveniseffectiveforslowcookingoflargeamontsoffood.
Thesecondkindofsolarovenisapanelcooker.Itincludesseveralflatwalls.orpanels.thatdirectlyreflectthesun’slightontothefood.Thefoodisinsideaseparatecontainerofplasticorglassthattrapsheatenergy.Peoplecanbuildpanelcookersquicklyandwithveryfewsupplies.Theydonotcostmuch.InKenyaforexamplepanelcookersarebeingmanufacturedforjusttwodollars.
Thethirdkindofsolarovenisaparaboliccooker.Ithasroundedwallsthataimsunlightdirectlyintothebottomoftheoven.Foodcooksquicklyinparabolicovens.Howeverthesecookersarehardtomake.Theymustbere-aimedoftentofollowthesun.Paraboliccookerscanalsocauseburnsandeyeinjuriesiftheyarenotusedcorrectly.
Youcanmakesolarovensfromboxesorheavypaper.Theywillnotcatchfire.Paperburnsattwohundredthirty-twodegreesCelsius.Asolarcookernevergetsthathot.Solarovenscookfoodatlowtemperaturesoverlongperiodsoftime.Thispermitspeopletoleavefoodtocookwhiletheydootherthings.
72.Whatisthemainpurposeoftheauthorinwritingthepassage?
A.Totellthereadershowtomakesolarovens.
B.Toadvertisethesolarovens.
C.Togivethereadersbriefintroductionofsolarovens.
D.Tohelpreaderstosavecostonfuel.
73.Accordingtothepassagewecanconcludethat______.
A.panelcookeristhecheapestovenofthethree