【Moreandmorescientificexperimentsprovethatphysicalexercisecanreducethedangersofsomeillnessesinmiddle-agedpersons．Exercisestrengthenstheheartmuscle，reducesbloodpressureandhelptopreventmusclesfromchanginginto】

　　Moreandmorescientificexperimentsprovethatphysicalexercisecanreducethedangersofsomeillnessesinmiddle-agedpersons．Exercisestrengthenstheheartmuscle，reducesbloodpressureandhelptopreventmusclesfromchangingintofat．Physicalexerciseisjustasimportantforchildren．

　　Exerciseandfoodaffectgrowingspeedinyounglabanimals．Babymicestartrunningassoonastheyarebigenoughtouseanexercisewheelintheircage．If theygetextrafoodandrunalot，theywillgrowasmuchas1.5timesbiggerthannormal．

　　Thesamedifferencesingrowingspeedmightbefoundbetweenactiveandinactivechildren．Physicalexercisehelpsactivechildrengrowfasterthaninactivechildren．Oneexperimentshowsthatthebrainsofthemicethathadenoughexerciseweighedabout3％morethanthoseofthemicethatdidnotexerciseThemicethatexercisedaremuchquickertolearndoingnewexercisethanthemicethatdidnotexercise．

　　Theresultsoftheexperimentssupposethetheorythatexercisecanhelpbabieslearntotalkandwalksoonerthanexpected．

　　Thegoodeffectsofphysicalexercisearenotlimitedtochildrenandmiddle-agedpeople．Exercisecontinuestobeanimportantpartofourlivesafterwegrowold．Forexample，peopleover50yearsoldbegintolosecalcium(钙)fromtheirbones，whichgetweakerandcanbreakeasily．Physicalexercise，however，helpstostrengthenthebonesandtopreventthemfromlosingcalcium．Ofcourse，oldpeoplecantakemedicinestopreventthemselvesfromsufferingfromlosingcalcium．Butthemedicinestheytakeincreasethechanceofdevelopingsomekindofcancer(癌)．Sophysicalexerciseisamuchsafertreatment(治疗)．

　　【小题1】Fromthepassageweknowthat .

　　A．miceneedtoeatmoreandexercisemoreB．childrenneedmoreexercisethanotherpeopleC．oldpeopleliketotakemedicinetotreattheirillnessesD．middle-agedpeopleareeasytogetfat【小题2】Activechildren thaninactivechildren．A．enjoywalkingmoreB．areclevererandhealthierC．arestrongerbutmorefoolishD．areclevererbutweaker