【Theforestsofthetropicsproduceamagnificentgrowthoftrees,butcommerciallumberingisinhibitedbyproblemsthatincreasethecostofremoval.Theproliferationofspeciesthatiscommontoalltropicalforestscreatesdifficultiesbecausemany】

　　Theforestsofthetropicsproduceamagnificentgrowthoftrees,butcommerciallumberingisinhibitedbyproblemsthatincreasethecostofremoval.Theproliferationofspeciesthatiscommontoalltropicalforestscreatesdifficultiesbecausemanyspeciesareworthless.Thelumbermancombstheforest,therefore,removingthevaluabletreesthatareconvenienttowaterways,andfloatingthemdownstreamtoasawmill.Unfortunately,tropicalhardwoodstendtogrowslowly;anareaonceclearedneedssubstantialtimetorecover,forcingthesawmillstobecomemobile.Distancetomarkettendstobeconsiderable,raisingcostsoftransport.Becauseofthesedifficulties,onlythemostvaluablewoodscanabsorbthehighcostsassociatedwithproduction.Othertreesareleftuntouched.

　　1.Accordingtothepassage,oneoftheproblemsofcommerciallumberingis____.

　　A:selectingvaluabletreesisdifficult

　　B:manyofthetreesareuselessfortimber

　　C:thereislittlevarietyinthetypesoftreesintheforests

　　D:veryfewhardwoodsgrowintheforests

　　2.Thelumbermensearchtheforestsforvaluabletreesandchoosetheonesthat____.

　　A:areneartorivers

　　B:matureveryslowly

　　C:aretropicalspecies

　　D:areeasytocutdown

　　3.Accordingtothepassage,thesawmillshavetobemobilebecausetheyare____.

　　A:transportednearthemarkets

　　B:floateduptherivers

　　C:usedtotransportwood

　　D:movedawayfromclearedareas

　　4.Accordingtothepassage,relativelyfewtreesareremovedfromtheforestsbecause____.

　　A:theproliferationofspeciescannotabsorbthehighcosts

　　B:thetropicalhardwoodsareexpensivetoproduce

　　C:itistooexpensivetotransportthehardwoods

　　D:onlythemostvaluablejustifythecost

　　5.Whatcanbeassumedfromtheinformationgiveninthepassage?

　　A:tropicalforestsproducetoomanytrees.

　　B:toomanyspeciesgrowintheforests.

　　C:notenoughspeciesgrowneartherivers.

　　D:usefulspeciesdonotreproducequickly.