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在平面直角坐标系xOy中，以坐标原点O为极点，x轴的正半轴为极轴建立极坐标系，已知线C的极坐标方程为：ρ=2sin（θ+），过P（0，1）的直线l的参数方程为：（t为参数），直线l与曲线C交于M，N...
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高二下学期数学《》真题及答案
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若曲线的极坐标方程为ρ＝2sinθ＋4cosθ以极点为原点极轴为x轴正半轴建立直角坐标系则该曲线的直
在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立极坐标系.曲线C.1的参数方程为t为参数曲
在极坐标系中曲线C.1和C.2的方程分别为和＝1以极点为平面直角坐标系的原点极轴为x轴的正半轴建立平
在直角坐标系xOy中以O.为极点x轴正半轴为极轴建立极坐标系曲线C.的极坐标方程为曲线C.的直角坐标
在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立极坐标系.若P.点为直线ρcosθ-ρsi
在平面直角坐标系xOy中直线l的参数方程为k为参数以原点O.为极点以x轴正半轴为极轴与直角坐标系xO
在直角坐标系xOy中曲线C.1的参数方程为α为参数在极坐标系与直角坐标系xOy取相同的长度单位且以原
选修4-4坐标系与参数方程在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立极坐标系已知射线
选修4—4坐标系与参数方程在平面直角坐标系xOy中已知曲线C.的参数方程为.以直角坐标系原点O.为极
在平面直角坐标系xoy中圆C.的参数方程为t为参数.在极坐标系与平面直角坐标系xoy取相同的长度单位
在直角坐标系xOy中曲线M.的参数方程为α为参数若以直角坐标系中的原点O.为极点x轴的正半轴为极轴建
选修4—4坐标系与参数方程在平面直角坐标系xOy中已知曲线C.的参数方程为.以直角坐标系原点O.为极
在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立坐标系.已知射线θ＝与曲线t为参数相交于A
在平面直角坐标系xOy中直线l的参数方程为t为参数P.Q.分别为直线l与x轴y轴的交点线段PQ的中点
在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立极坐标系.若极坐标方程为ρcosθ＝4的直
已知直角坐标系xOy中直线l的参数方程为.以直角坐标系xOy中的原点O.为极点x轴的非负半轴为极轴圆
在平面直角坐标系xoy中已知直线l的参数方程为参数t∈R.同时在以坐标原点为极点x轴的正半轴为极轴建
在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立极坐标系.已知射线θ＝与曲线t为参数相交于
在平面直角坐标系xoy中已知曲线C.的参数方程为α为参数现以O.为极点x轴的正半轴为极轴建立极坐标系
在直角坐标系xOy中以原点O.为极点x轴的正半轴为极轴建立极坐标系.曲线C.1的参数方程为t为参数曲
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对下列现象的微观解释不正确的是
如图所示传送带的右边平滑对接倾角为30°的光滑固定的斜面左边对接固定的挡板传送带ab的长度l＝2.0m它始终以v＝3.0m/s的速度顺时针转动．现将一个可视为质点的小物体由c点静止释放bc距离L＝1.4m小物体与传送带表面的动摩擦因数取g＝10m/s2．求 1小物体运动到传送带的下端a点时的速率 2若小物体与挡板相撞时无机械能损失试通过计算说明小物体能否与挡板发生第二次相撞．
以下说法正确的是
Thetermtoextendanolive橄榄branchmeanstomakeanofferofpeaceorreconciliation和好.ThistermhasBiblicalshèng jīng 的originscomingfromthesectionoftheOldTestamentthatdealswiththefloodthesignthatthefloodisoverisanolivebranchbroughtbacktotheark方舟byadove.OlivebrancheswerealsosymbolsofpeaceinAncientGreeceandRomeandtheycontinuetobeusedinvariousworksofartthataremeanttosuggestpeace. Somepeoplehavesuggestedthattheolivewasaverydeliberateandwell﹣consideredchoiceasametaphor比喻forpeacebecauseolivetreesfamouslytakeyearstomature.Waristypicallyveryhardonthetreesbecausepeoplecannottakethetimetonurturethemandplantnewones.Thereforetheofferofanolivebranchwouldsuggestthatsomeoneistiredofwarwhetheritisanactualwarorafallingoutbetweenfriends. InAncientGreekandRomantimespeoplewouldofferactualolivebranches.InRomeforexampledefeatedarmiestraditionallycarriedolivebranchestoindicatethattheyweregivinginandtheGreeksusedthemintoweddingsandotherceremonies.Inthemodernerathebranchisusuallymetaphoricalratherthanactualnotleastbecausetheplantscanbeabitdifficulttoobtain. Manypeopleagreethatpeacenegotiationsatalllevelsofsocietyareagoodidea.Betweennationsobviouslyitisimportanttoextendanolivebranchtoensuremutualsafetyandtohelptheworldrunmoresmoothly.Thisactcanalsobeimportantonapersonallevelasresolvingconflictandlearningtogetalongwithothersisviewedasanimportantlifeskillinmanycultures. Atsomepointintheirlivesmanypeoplewillbeadvisedtoextendanolivebranchtosettleadisputeorresolveanissue.Somepeoplebelievethatittakesanimmenseamountofcouragetotakethisactionasitoftencomeswithanadmissionofwrongdoingandregret. 32.AccordingtotheBible. A.anolivebranchsuggestsfloodiscoming B.thearkismadeofolivetreewood C.anolivebranchmeansfloodisover D.adovelovestosettleontheolivebranch 33.TheoliveisconsideredagoodchoiceasametaphorforpeaceforthefollowingreasonsEXCEPT. A.olivetreesfamouslytakeyearstomature B.olivebranchesmakepeopletiredofwar C.waristypicallyveryhardonthetrees D.peoplecannottakethetimetonurturethemwhileatwar 34.Whyareactualolivebranchesseldomusedinmoderntimes? A.Olivetreesarebeingprotectednow. B.Olivetreesareplantedonlyincertaincountries. C.Olivetreescanbefartoseek. D.Thereisnoneedtouserealolivebranches. 35.Itcanbelearnedfromthetextthattoextendanolivebranch. A.isnotimportantonapersonallevel B.isonlyimportantbetweennations C.takesalotofcourage D.isanimportantlifeskillinmanycultures.
人类的活动离不开能源人类的生存离不开水资源． 1目前人们使用的主要能源是煤天然气．近年来科学家陆续发现海底埋藏着大量的将来可能会代替化石燃料的新能源这种新能源是． 2我国部分地区的饮用水来自河水河水在净化处理时加入明矾的作用是．在日常生活中若要鉴别净化后的水是硬水还是软水最简单的方法是加入进行检验．
Listedherearefourofthethousandsofimpressivemuseumsaroundtheworld. TheGuggenheimMuseumBilbaoinBilbaoSpain Builtin1997theGuggenheimMuseumBilbaoisoneofthenewestintheworld.IthastransformedtheindustrialcityofBilbaointoatraveler'sdesireddestination.Thebeautifularchitectureofthemuseumhasprovidedadramaticbackgroundformoviesandcommercials. TheLouvreinParisFrance ProbablythemostfamousLouvrealsoholdsthemostfamouspaintingintheworldtheMonaLisabyLeonardodaVinci.Crowdscanbefoundanydaysurroundingthesmallbutmysteriouspaintingofthesmilingwoman.ButtheLouvreismuchmorethanahometotheMonaLisa.TheLouvreisvisitedbymorepeopleeachyearthananyothermuseumintheworld. TheBarnesFoundationinPhiladelphiaAmerica Justopenedinitsnewdowntownlocationin2012theBarnesFoundationisuniqueinthatitisacompletelyreproduceddisplayfromoneman'sprivatecollection.Dr.AlbertC.Barnesstartedcollectingartintheearly20thcenturyandcollectedamongothersthelargestnumberoforiginalRenoirpaintingsintheworld. TheUffiziGalleryinFlorenceItaly Walkingonthemarbledfloorsfeelslikesteppingbackintime.Thebuildingitselfisabeautifulpalace﹣likestructurewithfrescoes湿壁画decoratingtheceilingsandwalls.Viewersarebowledover印象深刻bytheworksbyBotticellisuchasTheBirthofVenus.Classicartworksfromnearly1000yearsagodescribereligiouseventsofthetime. 21.Whichofthefollowingisthemostpopular? A.TheLouvre. B.TheGuggenheimMuseumBilbao. C.TheBarnesFoundation. D.TheUffiziGallery. 22.WhatmakestheBarnesFoundationparticular? A.Itsstructure. B.Itscollection. C.Itslocation. D.Itshistory. 23.Whattypeofwritingisthistext? A.Anactivityposter. B.Anexhibitionannouncement. C.Anartshowreview. D.Atravelguide.
Ihadbeenstaringatthewhitewallsofthevideogamestoreforabout2hourssincelunch.Itwasavery41day.Iglancedatthetableinfrontofthestoreandmyheart42.ItwasthedonationtableforthevictimsofTyphoonYolandaandeventhoughIhaddonatedwhatIcouldI43feltsadwheneverIsawthepeopleontheTVsuffering. Iwasbrokenoutofmy44whenthedoorsgotopen.Customers45! Shewasasmallgirlabout10or11.Hermotherwasaccompanyingherwithafewplasticbags.I46hermom.WhenIwassellingcigarettesonthestreetIsawhersellingclothesshe47herselfatthemarket. Thedaughterjusthada48andhermomfinallyhad49moneytobuyaPS3andsomegames. Thegirlhalf﹣joggedhalf﹣skippedtomycounter.She50herbackpackandpulledoutaconsole操纵板.Hermomhandedmethebagfullofgames. CanI51this? Suresweetienoproblem. Iinspectedtheconsoleandthegamesandnothingwasopened.Accordingtoour52Ireturnedthe53tothemom.Shehandedittothegirl.Andthegirlranoffasfastasherlittlefeetcouldtakeher.Iwasabouttoaskwhenthemomseeingmy54explainedShewantstosellherbirthday55soshecandonatetothe56. Shewas57togiveupwhatwassupposedtobehersandgavetothose58.That'srealgenerosityoutthere. 59IwaswatchinghertalkingtothegirlatthedonationstableIwasremindedthateventhoughtherearealotof60peopleintheworldtherearestillthosepeoplejustlikethatlittlegirl. 41.A.good B.cold C.warm D.slow 42.A.beat B.ached C.ran D.sank 43.A.almost B.also C.still D.never 44.A.moods B.dreams C.pains D.thoughts 45.A.firstly B.finally C.quickly D.excitedly 46.A.greeted B.found C.recognized D.told 47.A.wore B.made C.washed D.bought 48.A.date B.job C.birthday D.disease 49.A.enough B.little C.easy D.big 50.A.carried B.opened C.sold D.left 51.A.buy B.change C.return D.donate 52.A.plan B.decision C.discussion D.regulation 53.A.money B.backpack C.games D.receipt 54.A.smile B.expression C.unhappiness D.difficulty 55.A.card B.cake C.surprise D.gift 56.A.victims B.workers C.charities D.typhoons 57.A.grateful B.willing C.unhappy D.afraid 58.A.poor B.unfortunate C.indanger D.inneed 59.A.Since B.Until C.While D.Although 60.A.selfish B.unlucky C.poor D.rich
假定你是李华是你校读书俱乐部的负责人计划在下个月组织英语读书节. 请给你的美国笔友Tony写信介绍本次活动并请他为本次读书节推荐阅读书目. 注意 1.词数100左右 2.可以适当增加细节以使行文连贯 3.信的开头和结尾已给出不计入总词数. DearTony Lookingforwardtoyourearlyreply! Yours LiHua.
设想在深太空探测中一个探测器到达深太空中的一颗外星球不考虑自传开始探测实验．首先测出在外星球近地环绕的周期为T着陆后竖直上抛一个小球用速度传感器测出上抛的初速度v用秒表测出落回抛出点的时间t则根据上述测量的量不能算出的物理量是
在竖直向上的匀强电场中有两个质量相等带异种电荷的小球AB均可视为质点处在同一水平面上现将两球以相同的水平速度v0向右抛出最后落在水平地面上运动轨迹如图所示两球之间的静电力和空气阻力均不考虑则
小明同学对所学的部分化学知识归纳如下其中的错误的是
下列叙述不正确的是
小亮用固体氯化钠配制80g溶质质量分数为10%的氯化钠溶液有关他的实验操作下列说法正确的是
如图是教案备课库中常见物质间的相互关系．其中ABCDE是五种不同类别的物质EF的类别相同CM的组成元素相同C呈固态时俗称“干冰”．图中“﹣”表示两端的物质间能发生反应“→”表示物质间存在转化关系反应条件部分反应物和生成物已略去． 1写出M的一种用途． 2写出B的化学式． 3写出F→D的化学方程式． 4写出E→D的实验现象． 5图示相互关系中没有涉及到的基本反应类型是．
根据下列图示回答相关问题 1氟的相对原子质量为氟元素的化学性质与图2中填字母序号化学性质相似． 2图3是某化学反应微观示意图．在点燃条件下A和B反应生成C和D． ①1个B分子中含有个原子．②A中氮元素和氢元素的质量比为． ③在该反应中生成C和D的质量比为．计算结果用最简整数比表示
如图所示电路中a点电势为3Vb点接地电阻R1R2＝15电容器电容C为3pF开始时ap相接电路处于稳定状态．现在断开ap连接bp直至电路重新稳定则在这一过程中
假定英语课上老师要求同桌之间交换修改作文请你修改同桌写的以下作文.文中共有10处语言错误每句中最多有两处.每处错误仅涉及一个单词的增加删除或修改. 增加在缺词处加一个漏字符号∧并在其下面写出该加的词. 删减把多余的词用斜线\划掉. 修改在错词下面划一横线并在该词下面写出修改后的词. 注意1.每处错误及其修改均仅限一词 2.只允许修改10处多者从第11处起不计分. LastFridayourschoolorganizedustoafirestationwhatwehadexpectedforseveralday.Whenwegottherethefire﹣fighterswelcomedusbutledusintoanexhibitionhall.Thereoneofthemdeliveredthelectureonfirecontroltous.Afterthattheyshowushowtooperateafireextinguisherandevengaveourchancestopractiseusingit.NowIdaresayIcanuseitskillful!Onourwayhomewecouldn'thelptotalkingaboutwhatwehadexperienced.Wefeltveryhappyandexcitedbecausewehadgainedsomanyknowledgeaboutfirecontrolandknownwhattodoanemergency.
MobilephonesandiPadsarenowwonderfultoolsforlearningandteachingEnglish.Withthehelpofthethousandsofeducationandlanguageappsavailableonlinestudentscanmakeeffectiveuseofthemtolearninaninteractiveenvironment.GivenbelowisalistofsomeofthebestappsforlearningandteachingEnglish. GrammarUp GrammaristheheartofanylanguageandthustheGrammarUpappisoneofthemosthighlyrecommendedappsforEnglishlearners.Thisappisspecificallydesignedforpeoplewhowanttoimprovetheirgrammarvocabularyandwordselection.Itconsistsofmorethan1800multiple﹣choicequestionsgroupedundertwentydifferentgrammarcategories. iFPoems iFPoemsisafantasticappforpoetrylovers.Thisappconsistsofagreatcollectionofpoemsfromfamouspoetsaroundtheworld.Italsoallowsuserstosavetheirfavoritesalongwithrecordingtheirownreadingsofthepoems. iBooks iBooksisacompletebooklibraryfortheiPadusers.ItincludestheiBookstoreandallowsuserstodownloadandreadbooks.Theappfeaturesabeautifulbookshelfonwhichyoucanbrowsevariousbooksorevenaddnotestoyourfavoriteparagraphsinthebook.Youcanalsocreateyourowntextsanduploadthemintotheapp. SpeakingPal RecommendedasoneofthebestappsforEnglisheducatorsandlearnersSpeakingPalallowsyoutorecordyourspeechandcompareitwithanativeEnglishspeaker.ThisamazingappcombinesvideowithautomaticspeechrecognitionsoftwarethattestsyourEnglishspeakingskills.YoujusthavetospeakwithavideocharacterandgetimmediateresponseonhowwellyouspeakEnglish. 21.Whatdotheseappshaveincommon? A.Theycanbefoundonline. B.Theyarefreeofcharge. C.Theyimproveusers'grammar. D.They'redesignedbyteachers. 22.WhatcanwedowithiBooks? A.Downloadbooksforfree. B.Writenotesonitwithpens. C.Savenotesandtexts. D.Createabookstore. 23.WhatisspecialaboutSpeakingPal? A.Itoffersvideocallservice. B.Itevaluatesusers'speech. C.Itofferstalkswithanativespeaker. D.ItincludesEnglishspeakingcontests.
InformationOverload Inmodernsocietyifwe'retryingtomakeadecisionweoftenhavesomuchinformationthatwegetconfusedandwedon'tknowwhattodo.Thisstateisknownasinformationoverload.36Itcancausestressfrustrationandreducedproductivity.Butwhatcanwedointhefaceofinformationoverload? •Planforonlyonetimeeachdaytochecke﹣mailsocialmessagingsiteschatroomsetc.Don'tallowyourselftocheckmultipletimesunlessyoutrulyarewaitingforanimportante﹣mail.37Andthateatsupyourvaluabletimebeforegettingaway. •Ifyouaresufferingfromtoomanyelectronicinterruptionsduringtheweekdayaskpeopletocallortextyouduringworkhoursonlyifit'sreallyanemergency.38 •Remindyourselfthatit'sokaytonotknoweverything.Infactit'simpossibletokeepupwiththepaceoftheinformationsuperhighway.Thesooneryouacceptthatthehappieryou'llbe.39Itisgoodtofallbehindontheinformationthatreallyisn'tworthyourattention. •40Setasidearegulartimeeachweekwhereyouandotherfamilymembersdonotuseanykindofelectronicmediatechnologiesincludingtelevision.Itcouldbesomethingyoudoeveryweekendorperhapsanhourortwoeveryevening. A.Justcatchupwiththehappiestmoment. B.Knowwhat'sworthknowingandwhatisn't. C.Almosteveryonesuffersfromittosomedegree. D.Spendtimewithyourfamilyfreefromelectronicproducts. E.Weneedtofindsomeeffectivewaystoprocesstheinformation. F.Eachtimeyougoonlineyouruntheriskofbeingaddictedtoit. G.Otherwisetheyandyouendupstealingtimefromyouremployer.
下列过程中一定发生化学变化的是
Abalanceddietmeansthenutritionofthreemealsinadayshouldbebalancedandbreakfastisveryimportanttoachievethatgoal.Skippingbreakfast61causedamagetohealthapartfromreducingworkperformance.62studyhaveshowedthatifapersondoesnoteatbreakfast63regularheorshewillbe64ahigherriskofvariousdiseases. Howevermanypeopledonoteatbreakfast.Arecentsurveyshowsthat8.6percentofpeopledonoteatbreakfasteveryday.Thesituationiseven65badinpoverty﹣strickenareas. Whilemostpeopleareusedto66eatbreakfastthequalityoftheirmealisinquestion.About25percentofpeopledonoteatahomemadebreakfast67morethan80percentofpeopledonotconsumeahealthybreakfast. Childrenwomenandpeoplelivinginpoverty﹣strickenareasaremostlikelytobeaffected68itcomestoeatingunhealthybreakfasts.Howeveroldpeople69ageabove60tendtohavehealthybreakfastbecausethisgroupmostlyretiredhavetimeand70patienttocookbreakfastthemselves.
请用化学用语填空． 13个镁离子 2氦气 3标出NH4NO3中加点元素的化合价．
Inagrarian农业的pre﹣industrialEuropeyou'dwanttowakeupearlystartworkingwiththesunrisehaveabreaktohavethelargestmealandthenyou'dgobacktoworksaysKenAlbalaaprofessorofhistoryattheUniversityofthePacific.Laterat5or6you'dhaveasmallersupper. Thiscomfortablecycleinwhichtherhythmsofthedayhelpedshapetherhythmsofthemealsgaverisetothecustomofthelargemiddaymealeatenwiththeextendedfamily.MealsarethefoundationofthefamilysaysCaroleCounibanaprofessoratMillersvilleUniversityinPennsylvaniasotherewasaveryimportantinterconnectionbetweeneatingtogetherandstrengtheningfamilyties. Sinceindustrializationmaintainingsuchaslowculturalmetabolismhasbeenmuchharderwiththelongmiddaymealshrinkingtowhatevercouldbestuffedintoalunchbucketorboughtatafoodstand.Certainlytherewerebenefits.Moderntechniquesforproducingandshippingfoodledtogreatervarietyandquantityincludingatremendousincreaseintheamountofanimalproteinanddairyproductsavailablemakingusmoreenergeticthanourancestors. Yetplentyhasbeenlosttooeveninculturesthatstilllivetoeat.TakeItaly.It'snosecretthattheMediterraneandietishealthybutitwasalsoajoytoprepareandeat.ItalianssaysCounihantraditionallybeganthedaywithasmallmeal.Thebigmealcameataround1p.m.Inbetweenthemiddaymealandalatesmallerdinnercameasmallsnack.Todaywhentimezoneshavelessandlessmeaningthereislittletoleranceforoffices'closingforlunchandworseningtrafficincitiesmeansworkerscan'tmakeithomeandbackfastenoughanyway.Sotheformerlysmallsupperaftersundownbecomesthebigmealofthedaytheonlyoneatwhichthefamilyhasachancetogettogether.TheeveningmealcarriesthefullburdenthatusedtobespreadovertwomealssaysCounihan. 24.WhatdoesProfessorCaroleCounihansayaboutpre﹣industrialEuropeanfamilieseatingmealstogether? A.Itwashelpfultomaintaininganation'stradition. B.Itbroughtfamilymembersclosertoeachother. C.Itwascharacteristicoftheagrarianculture. D.Itenabledfamiliestosavealotofmoney. 25.WhatdoesculturalmetabolismLine1Para.3referto? A.Evolutionaryadaptation. B.Changesinlifestyle. C.Socialprogress. D.Paceoflife. 26.Whatdoestheauthorthinkofthefoodpeopleeattoday? A.Itsqualityisusuallyguaranteed. B.Itisvariedabundantandnutritious. C.Itismorecostlythanwhatourancestorsate. D.Itsproductiondependstoomuchontechnology. 27.WhatdoestheauthorsayaboutItaliansoftheolddays? A.Theyenjoyedcookingaswellaseating. B.Theyateabigdinnerlateintheevening. C.Theyatethreemealsregularlyeveryday. D.Theywereexpertatcookingmeals.
用如图所示的装置可验证机械能守恒定律直径为d的摆球A拴在长为L的不可伸长的轻绳一端L＞＞d绳的另一端固定在O点O点正下方摆球重心经过的位置固定光电门B．现将摆球拉起使绳偏离竖直方向θ角时由静止开始释放摆球当其通过最低位置时光电门B记录的遮光时间为t． 1摆球通过最低点的速度v＝用题中字母表示 2写出满足机械能守恒的表达式用题中字母表示
Longschoolholidayshelpstudentscleartheirheadsrelaxalittleandstretchtheirbrainsindifferentways. Traditionallyschoolingscheduleshavelongbeenbasedmoreontheneedsofsocietythanonefficienteducationstrategies.ForinstanceinIcelanditwastraditionallyarrangedtoallowchildrentohelpoutwithharvest.Othercountrieshavelongsummervacationsbecauseitissimplytoohottostudy.Inotherareaswherereligionplaysanimportantroleintheholidayseasonthereligioncalendarthencallsforthebreaksothatstudentscanhaveampletimetoparticipateinthereligiousceremoniesandtraditionsofseasonalholidays. Therearesomeobviousadvantagestoavacationthatlastslonger.Familieswholivealongdistancefromrelativesareabletotraveltogethersometimesacrosstheoceaninordertoconnectwiththeirlovedones.Evenifthereisnovisitingfamilyfarawayalongholidayisagreatopportunityforkidstointeractwiththecommunity.Fromaneducationalpointofviewachildthatisabletoexperienceanotherculturecangainvaluablelanguagehistoryandsocialskills. Longschoolholidaysarealsoneededinschoolsthathavebecomeoverlyacademicandtooexam﹣focusedinrecentyearswhichrequiresaconsiderablylongerholidaybreakfromsuchamarathonpumping灌输ofknowledgeanditmakesgreatsense! GreatpsychologistslikeFreudandPiagethavestressedplay'scentralroleintheformationoffully﹣rounded全面发展的individualssothelongholidayachievesthisbyallowingstudentstoexploretheworldoutsideschool.Thestudentsgettoparticipateinactivitiesthatwouldbedifficulttododuringaregularschoolterm. Asaconsequencelongschoolholidaycanbequiteconstructivetoourstudents! 28.Whattraditionallydeterminesthearrangementofschoolholidays? A.Localneeds. B.Culturalactivities. C.Religiouscustoms. D.Academicperformance. 29.Whichisoneoftheadvantagesoflongholidays? A.Studentsrunawayfromexams. B.Childrencanlearnscienceandhistory. C.Fewercoursesarerequiredatschool. D.Familybondsarestrengthened. 30.FreudandPiagetmayprobablyagreethat. A.schoolsneedlongerholidays B.holidayactivitiesarenecessary C.playismoreimportantthanlearning D.studentsshouldtravelaroundtheworld 31.Whatisthebesttitleofthepassage? A.TraditionalSchoolHolidays B.ActivitiesforLongHolidays C.BenefitsofLongHolidays D.AdvicefromPsychologists.
一列波沿x轴正向传播t＝0时刻的波形如图所示其中EF两点相对平衡位置的位移相同从该时刻起E质点回到平衡位置的最短时间为0.05s．F质点回到平衡位置的最短时间为0.15s质点的振幅为A＝10cm则下列说法正确的是
按照氢原子的能级图下列说法正确的是
某兴趣小组利用下列仪器进行气体的制取实验请分析回答下列问题 1仪器B的名称是． 2用高锰酸钾制取一瓶较纯净的O2应选用图中的仪器是填字母序号反应的化学方程式为． 3实验室用仪器ABCEF组合还可以制取的另一种气体是检验该气体的化学方程式为．
如图是磁流体发电机的示意图在间距为d的平行金属板AC间存在磁感应强度为B方向垂直纸面向外的匀强磁场两金属板通过导线与滑动变阻器相连变阻器接入电路的电阻为R．等离子体连续以速度v平行于两金属板垂直射入磁场理想电流表A的读数为I发电机内阻为r则
取碳酸钠样品含少量氯化钠杂质加入烧杯中滴加一定质量的稀盐酸至恰好完全反应时得到4.4g二氧化碳气体和100g溶质质量分数为14.1%的氯化钠溶液．请计算 1稀盐酸中溶质的质量． 2原混合物中碳酸钠的质量分数．结果精确到0.1%
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