Treesshouldonlybeprunedwhenthereisagoodandclearreasonfordoingsoand, fortunately,thenumberofsuchreasonsissmall.Pruninginvolvesthecuttingawayofovergrownandunwantedbranches,andtheinexperiencedgardenercanbeencouragedbythethoughtthatmoredamageresultsfromdoingitunnecessarilythanfromleavingthetreetogrowinitsownway. First,pruningmaybedonetomakesurethattreeshaveadesiredshapeorsize.Theobjectmaybetogetatreeoftherightheight,andatthesametimetohelpthegrowthofsmallsidebrancheswhichwillthickenitsappearanceorgiveitaspecialshape.Secondly,pruningmaybedonetomakethetreehealthier.Youmaycutdiseasedordeadwood,orbranchesthatarerubbingagainsteachotherandthuscausewounds.Thehealthofatreemaybeencouragedbyremovingbranchesthatareblockingupthecentreandsopreventingthefreemovementofair. Oneresultofpruningisthatanopenwoundisleftonthetreeandthisprovidesaneasyentryfordisease,butitisawoundthatwillheal.Oftenthereisaracebetweenthehealingandthediseaseastowhetherthetreewillliveordie,sothatthereisaperiodwhenthetreeisatrisk.Itshouldbetheaimofeverygardenertoreducewhichhasbeenprunedsmoothandclean,forhealingwillbesloweddownbyroughness.Youshouldallowthecutsurfacetodryforafewhurtsandthenpaintitwithoneofthesubstancesavailablefromgardenshopsproducedespeciallyfor thispurpose.Pruningisusuallywithoutinterferencefromtheleavesandalsoitisveryunlikelythatthecutsyoumakewillbleed.Ifthisdoeshappen,itis,ofcourse,impossibletopaintthemproperly. ?Whatwastheauthor'spurposewhenwritingthispassage?
A.To give practical instruction for pruning a tree.
B.To give a general description of pruning.
C.To explain how trees develop diseases.
D.To discuss different methods of pruning.
正确答案是A