大学英语四级阅读理解试题及答案.

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1、-大学英语四级阅读理解试题及答案（四）十六Treesshouldonlybeprunedwhenthereisagoodandclearreasonfordoingsoand,fortunately,thenumberofsuchreasonsissmall.Pruninginvolvesthecuttingawayofobergrownandunwantedbranches,andtheinexperiencedgardenercanbeencouragedbythethoughtthatmoredamageresultsfromdoingitunnecessarilythanfromle

2、avingthetreetogrowinitsownway.First,pruningmaybedonetomakesurethattreeshaveadesiredshapeorsize.Theobjectmaybetogetatreeoftherightheight,andatthesametimetohelpthegrowthofsmallsidebrancheswhichwillthickenitsappearanceorgiveitaspecialshape.Secondly,pruningmaybedonetomakethetreehealthier.Youmaycutdisea

3、edordeadwood,orbranchesthatarerubbingagainsteachotherandthuscausewounds.Thehealthofatreemaybeencouragedbyremovingbranchesthatareblockingupthecentreandsopreventingthefreemovementofair.Oneresultofpruningisthatanopenwoundisleftonthetreeandthisprovidesaneasyentryfordisease,butitisawoundthatwillheal.Oft

4、enthereisaracebetweenthehealingandthedeseaseastowhetherthetreewillliveordie,sothatthereisaperiodwhenthetreeisatrisk.Itshouldbetheaimofeverygardenertoreducewhichhasbeenprunedsmoothandclean,forhealingwillbesloweddownbyroughness.Youshouldallowthecutsurfacetodryforafewhursandthenpaintitwithoneofthesubs

5、tancesavailablefromgardenshopsproducedespeciallyforthispurpose.Pruningisusuallywithoutinterferencefromtheleavesandalsoitis--veryunlikelythatthecutsyumakewillbleed.Ifthisdoeshappen,itis,ofcourse,impossibletopaintthemproperly.1.Pruningshouldbedoneto______.--a.makethetreegrowtaller--b.improvetheshapeo

6、fthetreec.getridofthesmallbranchesd.makethesmallbranchesthicker2.Treesbecomeunhealthyifthegardener______.a.allowstoomanybranchestogrowinthemiddleb.doesnotprotectthemfromwindc.forcesthemtogrowtooquicklyd.damagessomeofthesmallsidebranches3.Whyisaspecialsubstancepaintedonthetree?a.Tomakeawoundsmoothb.

7、Topreventdiseaseenteringawoundc.Tocoveraroughsurfaced.Tohelpawoundtodry4.Agoodgardenerprunesatree______.a.atintervalsthroughouttheyearb.asquicklyaspossiblec.occasionallywhennecessaryd.regulareverywinter5.Wh