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化学源于生活． Ⅰ．化学实验﹣﹣“过滤”的原理与应用极具生活价值． （1）“筛子原理” 过滤即运用通常所说的“筛子原理（如图1）”：将 （填“溶液”或“悬浊液”）中的混合物质分离开来． ...
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InanewstudypublishedinjournalJAMAPaediatricsresearchersfoundtheamountoftimethatchildrenundertheageoftwospendlookingatscreensondigitaldeviceshasmorethandoubledovera17﹣yearperiod. Theteamtookalookbackatatimewhenmobilephoneusewasfarlesscommonthanitistodayassessingchildren'sscreentimein1997andthencomparingitto2014. TheresearchersusedstatisticspreviouslygatheredbytheChildDevelopmentSupplementPanelStudyofIncomeDynamicsattheUniversityofMichigananalysingdataregarding1327childrenin1997and443childrenin2014. AccordingtotheirfindingschildrenundertheageoftwointheUSwouldspendanaverageof1.32hoursinfrontofascreenonadailybasisin1997.By2014thisaveragehadincreasedto3.05hoursmorethandoublingover17years.Incomparisonchildrenagedbetweenthreeandfivespentanaverageoftwoandahalfhoursinfrontofscreensonadailybasisin1997.Thishadincreasedslightlytothreehoursadayby2014. ThereisgrowingconcernovertheamountoftimethatchildrenparticularlyveryyoungchildrenspendwatchingshowsandinfrontofscreenssaidWeiweiChenassistantprofessorintheDepartmentofHealthPolicyandManagement.Ourfindingsweresurprisingasitfeelslikemobiledevicesareeverywherebuttelevisionsarestillthemostcommonwayforyoungchildrentoconsumemedia.Furtherresearchisneededtoassesschangesinmediaconsumptionanddeviceuseinmorerecentyears. Expertswarnedthatvulnerablechildrencouldfacebecominglostindigitalspaceasthey'regrowingupwithoutenoughInternetsafetyeducation. 1Whatcanweknowaboutthenewstudy? A.Ittook17yearstoconduct. B.Itincludedchildrenbornin1997. C.Itcomparedstatisticsfromtwodifferentperiods. D.Itwasdonebytwoorganizationsworkingtogether. 2Howdidthedailyscreentimeofchildrenbetween3and5change? A.Italmostdoubled. B.Itreducedslightly. C.Itreached2.5hours. D.Itsawasmallchange. 3Whatsurprisedtheresearchers? A.ChildrenspentmoretimeonTVthanonmobiledevices. B.Digitaldevicesgainedmorepopularityamongchildren. C.Childrenstaredatscreensformuchlongerthanbefore. D.Digitaldevicesfailedtoattractyoungchildren. 4Whatisthebesttitleforthetext? A.ScreenTimeDamagesChildren'sHealth B.NewMethodsFoundtoReduceScreenTime C.ParentsInstructedtoLimitChildren'sScreenTime D.ChildrenunderTwoSpendTwiceLongeronScreens
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Chinesedragons龙arefictionalcreaturesarootofChinesepeoplewhoconsideredthemselvesasthedescendants后代ofdragons.SincetheircreationChinesedragons1winthedeeplovefromChinesepeoplebecauseof2theystrongpowerandsymbolicmeanings.Theyplayed3importantroleinthehistoryofChinesenationpoliticsreligioncultureandChineselanguageandbecameasymbolofChinaandChinesepeople. DragonisabeliefofChinesenationanda4goldChineseelement元素.WhenapersonhearsthenameofdragonChina5cometohisorhermind.Asthestrongestanimal6selectbyChinesepeopledragonhasthestrongestpower7helpsitgototheHeavenandtheHellandmakecloudandrains.Inancienttimesasabeliefdragongavestrongsupportstotherulingofabignationandtopeople'sfragilespiritsandhardlifebecausepeoplesufferedfromextremenaturaldisastersandlack8thesupportsfromscience.The9importantofdragontoChinesepeopleislikewatertocreaturesandit10reflectinpeople'sspiritbeliefsandideology.
下列是生活中一些常见物质的近似pH其中酸性最强的是
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易拉罐拉环拉断后就很难打开若将A4纸对折几次后用纸的硬尖角摩擦原拉环边缘如图所示一会儿罐口就会自动冲开并看到一团“白汽”．出现这团“白汽”是因为水蒸气发生了选填“液化”或“汽化”现象．摩擦后罐口会自动冲开是因为罐内气体对罐口拉片压力增大使罐口打开．
如图所示倾斜装置使液体和固体混合气球体积没有明显变化的是
A.changingB.availableC.exposureD.worsenE.sensitive F.densityG.restH.shadedI.refleciionsJ.interruptedK.fighting Areyoureyesdrywateryseeingdoubleor31tolightanddoyourbackandneckacheIfsoyouarelikelyoneofmanypeopletodaywhosufferfromdigitaleyestrain视疲劳alsocalledcomputer﹣visionsyndrome. Eyestrainisoftenrelatedtotheamountof32toscreensthedistancefromeyestoscreensandtheuseofmultiplescreensatthesametime.Howeverstudies havealsoshownthatthebluelightproducedbydigitaldevicesreachesfurtherintotheeyesthanotherkindsoflight.Thislightactuallyassisisattentionduringthedaybutcanresultin33sleeppatternsatnight. Scientistshavestatedthateyestrainisnotanecessaryevileveninamodernworldthatcirclesaroundtechnology.Sometimes34somesimpledetailsaboutyourrelativepositiontoscreenssuchasslayingabout60centimetersawaywillhelp.Alsoavoidoverheadandotherdirectsourcesoflightanduse35lampsandwindowblindswhilelookingatdigitaldevicesinstead. Beyondthewaysthatyourelatetodigitalscreenstherearealsowaystochangehowyouviewscreensthatarehelpfulin36eyestrain.Tobeginwithyourcomputerscreenshouldbehigh﹣resolution高分辨率andmayrequireascreentodecrease37.Alsobeawarethat''computerglasseswhichcutdownglare刺眼的光}andbluelightare38onthemarkect. Finallymanyofusfallintobadhabitswhileusiugdigitalscreensthatonly39theeffectsofeyestrain.Whenviewingdigitalscreensmanypeopleblink眨眼onethirdlessoftenthantheyusuallydo.Placeareminderonyourcomputertoblink!sothatyoureyesdon'tdryout.Also40youreyes'focusingmusclesbyusingthe20﹣20﹣20ruleevery20minutesfocusonsomething20feetawayfor20seconds. Therearemanyothermethodsusedtohelprelieveeyestrainsofindwhatworksforyouratherthangivingintotiredvision.
在元素周期表中镁元素的信息如图所示下列有关说法不正确的是
WiththeaveragenumberofchildreninaBritishfamilyfallingunderanaverageof2.0comparedwiththetraditional2.4childrenthepopulationoftheUKhasbeenfallingforquiteafewyears. Whyaren'tBritishpeoplehavingasmanychildrenastheyusedtoWelltherearemanyreasons.OneofthemisthatBritishpeoplearenowhavingtheirchildrenatamucholderagethanpreviouslymeaningtheyhavefeweryearsinwhichtheycanhavechildren.Mostyoungpeopletodaywantawell﹣paidjobsotheyoftengotouniversityafterhighschoolafteryearsofstudyatuniversitytheythenneedafewyearsofworkexperiencebeforetheycangetthejobtheywant.Soit'snotuntiltheyareabout30yearsoldthattheycanstarttothinkaboutsettlingdownandhavingchildren. AnotherreasonisthatitisrelativelyexpensivetobringupachildintheUK.Usuallybothparentsneedtoworktopayfortheirhomeandlivingexpenses.Theyneedtopaysomeonetolookaftertheirchildduringthedaywhichisexpensive. InadditionproblemsintheglobaleconomyoftenaffectBritishfamilies.Forexamplewhentimesaretoughandthereisaneconomicdownturnitbecomesdifficulttofindajoborkeeptheexistingone.Thiskindofuncertaintydiscouragespeoplefromhavinglargerfamilies. SowhatisBritaindoingtotryandsaveBritishfamiliesFirstofallthegovermmentistryingtomakeitcheapertohavechildren.Forexampletherehavebeenincreasesinmoneyfamiliescangainfromthestateeachmonth.Alsothereisanincreasingamountofmoneyfornurseryschoolssothatparentsdon'tneedtopaysomuchforchildcare.Inadditiontherearenowlawsallowingparentstotakemoretimeoffworksothattheycanlookaftertheirchildrenthemselvesratherthanhavingtopayotherstodoit. .
空气中含量较多且性质活泼的气体是
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