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一种树苗的成活率是90%，为保证成活450棵，至少要栽多少棵树苗？列式为（ ）
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一种树苗的成活率是95%为了保证成活380棵至少要种棵树苗．
去年3月12日某校学生参加植树活动在引江河两岸共栽ABC三种不同品种的树苗1500棵．今年植树节前同
红红家要栽种一批树苗这种树苗的成活率一般为75%﹣80%假如要栽活1000棵树苗那么至少应栽棵．
一种树苗的成活率是85%至90%要想保证成活180棵树至少要栽种棵树苗．
生态公园计划在园内的坡地上种植甲乙两种树需要购买这两种树苗共100棵.甲种树苗的成活率为96%乙种树
某地区林业局要考察一种树苗移植的成活率对该地区这种树苗移植成活情况进行调查统计并绘制了如图所示的统计
栽一种树苗成活率最低是50%最高是80%如果想保证种活2400棵树最少种树棵．
栽一种树苗成活率为94%为保证栽活470棵至少要栽树苗棵．
李刚家要栽种一批树苗这种树苗的成活率一般为80%如果要栽活1000棵树苗那么至少应栽棵．
栽一种树苗成活率为94%为保证栽活470棵至少要栽树苗棵．
一种树苗经试种成活率是88%为了保证种活900棵至少应栽种多少棵树苗得数保留整数
李刚家要栽种一批树苗这种树苗的成活率一般为75%﹣80%如果要栽活1200棵树苗那么至少应栽棵．
栽一种树苗成活率为94%为保证栽活470棵至少要栽树苗棵．
经实验一种树苗的成活率在70%～85%之间如果要保证成活595棵那么至少要栽树苗．
我市为绿化城区计划购买甲乙两种树苗共计500棵甲种树苗每棵50元乙种树苗每棵80元调查统计得甲乙两种
一种树苗经试种后成活率是95%为了保证成活380棵至少应种树苗棵．
300棵
400棵
450棵
一种树苗的成活率是90%为了保证种活360棵树至少要栽棵树苗．
一种树苗经试种成活率为98%为保证成活350棵至少应种棵．
为推进郴州市创建国家森林城市工作尽快实现让森林走进城市让城市拥抱森林的构想今年三月份某县园林办购买了
种植某种树苗这种树苗的成活率为0.9若种植这种树苗5棵用模拟试验的方法求恰好成活4棵的概率.
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Iwasdrowningindepression.SeveralmonthsagoI'd41allmysavingsandincomefrommyjob.SoImovedtoafarminthemountainshopingtoforgetmy42.HereIthoughteverythingwasgreyandIcouldn'tseeanyother43. Thenonedaythephoneranganditwasaladyontheotherend44purchasinghensanddirections.Igaveherthe45andsetupan46thefollowingmorning.AndthenshetoldmeaboutJackherlittleboywithautism自闭症.Shewantedto47himandIsaidyes. Thenat11a.m.thenextmorningacar48.IheadedforourgateandbeforeIcouldreachitalittleboywasrunningtowardsme49callingoutJanet﹣I'mJack.I50himcarryingadinosaurbook.Wewerecarriedoffintothefarmwithdinosaur51. Wereachedthehenarea.Jackchosethreebabyhensandhetoldthemthey'd52withhimforever.AsJackwaslettingthebabiesknowhowwellhe'd53themmyfancyblackroostercameuptous.IaskedJackifheeverheldaroosterand54Jackwassittingonapieceofwoodwiththeroosteronhislap55ofthemcooing咕咕叫ateachother. We56thehenswithJack'sparentsbehindus.JackandIweredeepin57aboutanimalsuntilwegottotheircar.FinallyIsaid58toJackandweallwaved. Thelightdrovedownmydriveway59somethingpleasantwasleftbehind.AndIheldontoJack'slightuntilIstarteda60lifeformeandmyanimals. 41.A.reduced B.spent C.preserved D.lost 42.A.memories B.worries C.fears D.challenges 43.A.sign B.shadow C.color D.design 44.A.askingabout B.decidingon C.insistingon D.puttingforwards 45.A.instruction B.opinion C.price D.information 46.A.schedule B.appointment C.business D.record 47.A.join B.comfort C.bring D.treat 48.A.stopped B.crashed C.brokedown D.droveoff 49.A.nervously B.shyly C.unwillingly D.excitedly 50.A.imagine B.remember C.recommend D.watch 51.A.statements B.origins C.stories D.reports 52.A.live B.play C.study D.wander 53.A.dealwith B.worryabout C.makeuseof D.takecareof 54.A.suddenly B.immediately C.slowly D.carefully 55.A.all B.none C.both D.neither 56.A.kept B.approached C.caught D.left 57.A.thought B.conversasion C.love D.life 58.A.sorry B.thanks C.goodbye D.hello 59.A.but B.as C.since D.for 60.A.successful B.healthy C.balanced D.new
如图所示电源电动势为E内阻为r电路中的R2R3分别为总阻值一定的滑动变阻器R0为定值电阻R1为光敏电阻其电阻随光照强度增大而减小当开关S闭合电容器中一带电微粒恰好处于静止状态下列说法中正确的是
请修改下面的短文.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. InDecember9anEnglishspeechcontestisheldinourcity.36studentsfrom15 schoolstookpart.ThecontestmadeupofthreeroundsanEnglishspeechanswering thequestionsandatalentshow.EverystudentmadeaexcellentspeechinEnglish whichthemewasaboutTheBeautyofOurCity.Whentheyansweredthequestions theyfeltconfidentlyofsucceeding.Inthetalentshowcolorfulperformancesgivenbyher weremorethanattractive.There'snodoubtaboutthatthiscontestwasahugesuccess. Throughtheactivitythestudentshavelearntalot.Theyhavenotonlyimprovedtheir speakingEnglishandalsoenjoyedasenseofachievement.
如图所示边长为L的正方形导线框abcd置于垂直纸面向里的匀强磁场中磁感应强度为B．线框绕固定轴OO′以角速度ω匀速转动已知线框每条边的电阻大小为R．ad两点用导线导线电阻不计与阻值为R的电阻连接不影响线圈的转动则通过该电阻电流的有效值为
“用DIS研究加速度与力的关系”的实验装置如图a所示实验中用所挂钩码的重量作为细线对小车的拉力F通过增加钩码的数量多次测量可得小车运动的加速度a和所受拉力F的关系图象他们在轨道水平和倾斜的两种情况下分别做了实验得到了两条a﹣F图线如图b所示． 1图线填“①”或“②”是在轨道右侧抬高成为斜面情况下得到的 2在轨道水平时小车运动的阻力Ff＝N 3图b中拉力F较大时a﹣F图线明显弯曲产生误差．为避免此误差可采取的措施是． A．调整轨道的倾角在未挂钩码时使小车能在轨道上匀速运动 B．在增加钩码数量的同时在小车上增加砝码使钩码的总质量始终远小于小车的总质量 C．将无线力传感器捆绑在小车上再将细线连在力传感器上用力传感器读数代替钩码的重力 D．更换实验中使用的钩码规格采用质量较小的钩码进行上述实验．
如图所示在xOy平面内存在均匀大小随时间周期性变化的磁场和电场变化规律分别如图乙丙所示规定垂直纸面向里为磁感应强度的正方向沿y轴正方向电场强度为正．在t＝0时刻由原点O发射初速度大小为υ0方向沿y轴正方向的带负电粒子．已知u0t0B0粒子的比荷不计粒子的重力． 1t＝时求粒子的位置坐标 2若t＝5t0时粒子回到原点求0～5t0时间内粒子距x轴的最大距离 3若粒子能够回到原点求满足条件的所有E0值．
如图所示固定的水平光滑金属导轨间距为L左端接有阻值为R的电阻处在方向竖直磁感应强度为B的匀强磁场中质量为m的导体棒与固定弹簧相连放在导轨上导轨与导体棒的电阻均可忽略．初始时刻弹簧恰处于自然长度导体棒具有水平向右的初速度v0．在沿导轨往复运动的过程中导体棒始终与导轨垂直并保持良好接触． 1求初始时刻导体棒受到的安培力． 2若导体棒从初始时刻到速度第一次为零时弹簧的弹性势能为Ep则这一过程中安培力所做的功W1和电阻R上产生的焦耳热Q1分别为多少导体棒往复运动最终将静止于何处从导体棒开始运动直到最终静止的过程中电阻R上产生的焦耳热Q为多少
如图甲所示理想变压器原线圈匝数n1＝2200匝副线圈匝数n2＝100匝电流表电压表均可视为理想交流电表定值电阻R＝10Ω二极管D正向电阻等于零反向电阻无穷大．变压器原线圈接人如图乙所示的交流电压下列说法正确的是
如图所示一端封闭内径均匀的玻璃管长为L＝1.000m中间有h＝0.150m的水银柱将一部分空气封闭在管内水平放置时A端空气柱的长度LA＝0.400m．把玻璃管在竖直平面内缓慢倒转到开口竖直向下后再把开口端B缓慢插入水银槽内直到A端空气柱的长度为0.375m且再次处于平衡状态为止．已知外界大气压p0＝75cmHg在整个过程中温度保持不变．求最后平衡时玻璃管内B端空气柱的长度结果保留三位小数．
质量为M＝1kg的木板静止在粗糙水平面上木板与地面间的动摩擦因数为μ1在木板的左端放置一个质量为m＝1kg大小可忽略的铁块．铁块与木板间的动摩擦因数为μ2取g＝10m/s2．若在铁块右端施加一个从0开始增大的水平向右的力F假设木板足够长铁块受木板摩擦力Ff随拉力F的变化如图所示．则两个动摩擦因数的数值为
某同学设计了一个电磁推动加喷气推动的火箭发射模型其工作原理如图所示．竖直固定在绝缘底座上的两根长直光滑金属导轨间距为L导轨间加有垂直导轨平面向里的匀强磁场B．绝缘火箭支撑在导轨间总质量为m燃料室中的金属棒EF电阻为R通过电刷与导轨保持良好接触．引燃装置下方的推进剂迅速推动刚性金属棒CD电阻可忽略且和导轨接触良好沿导轨向上运动在棒EF中激励出强电流产生电磁推力加速火箭经过时间△t回路CDFE面积减少△S火箭刚好脱离导轨．当火箭脱离导轨时电阻R产生的焦耳热使燃料燃烧形成高温__气体燃烧室下方的可控喷气孔打开喷出燃气进一步加速火箭．不计空气阻力不计导轨的电阻 1求△t时间内棒EF中感应电流的平均值I及火箭脱离导轨时的速度V0 2若火箭总质量m＝10kg脱离导轨时的速度V0＝20m/s喷气孔在极短的时间内向下喷出质量m′＝2kg的燃气燃气相对喷气后火箭的速度为u＝100m/s．求喷气后火箭的速度Vl及喷气过程燃料释放的内能Q 3在第2问中若喷气孔将m′＝2kg的燃气分两次喷出每次喷出燃气的质量为m′/2燃气相对喷气后火箭的速度均为u＝100m/s求喷气后火箭的速度V2．
AboutsixyearsagoItookajobsomepeoplewouldconsideradreamjob.Atthetimeitwasconsideredasecurejobwithgreatbenefits.AstheyearspassedIrealizedIwasjustrepeatingeveryday.SoIdecidedtobeginbuildingmyownbusiness. Iknowwhatyouarethinking﹣there'snosecurityinthat!YeahIknow.IhaveheardthatandaboutonethousandotherreasonswhyIshouldhavecontinuedworkingattheregularjob.ButIdon'tregretmydecision.Iknowmanypeopleouttherealsowanttostarttheirownbusiness.Herearesomethingsyouneedtoknowbeforebreakingthemouldandleavingyour9﹣5toconcentratefull﹣timeonyourdreamThere'sneveraperfecttime.Somethingwillalwayscomeuptopreventyoudefer推迟yourdecisionchangeyourminddiscourageyouorsetyoubackabouttenyears. Havinganexperiencedandtrustedadviserisimportant.Why?Becauseifyoufindonewithasimilarthoughtprocessitislikelythattheyhavewalkedinthepathyouaretaking.Payattentiontotheiradviceasitcansaveyourheartache. Havingallthedetailsfiguredoutisimpossible.Therearesomanythingsyouhavetodobeforelaunchingoutintothedeep.Eitherwaytherearerisksinvolved.Youcanhaveallofyourinsecuritiessolvedandguesswhat!Somethingwillcomeuptomakeamessofeverything.Keepmovingon.Pressthroughit. Theclosertheyarethedeepertheystab.Notallofyourfriendswillcelebrateyourchange.Therewillbethosewhowouldratherdiscourageyouandtellyouhowyouwillnevermakeitbutalltheywouldhavetodoissupportyou.It'syourdream.It'syourresponsibility.Ifyouallowthewordsofotherstokeepyoufromityouweren'tsuitableforit. 25.Whydidtheauthordecidetostarthisownbusiness? A.Hegotfedupwiththeregularjob. B.Hewasencouragedbypeoplearoundhim. C.Hethoughthispreviousjobwasoutofdate. D.Hedidn'tmakegoodmoneyfromtheregularjob. 26.Whatdoestheauthormeanbybreakingthemouldinthesecondparagraph? A.Notobeyingtherulesatwork. B.Learningnewwaystodothejob. C.Gettingoutoftheoldworkplace. D.Improvingtheworkingenvironment. 27.Whichstatementwilltheauthoragreewith? A.Preparationisn'tthatimportantinstartingabusiness. B.Oneshouldjustdoitifhewantstostartabusiness. C.Moredetailsshouldbeconsideredtoreducerisks. D.Oneshouldtakeothers'wordsseriously. 28.What'stheauthor'spurposeinwritingthetext? A.Toexplainwhyhestartedhisownbusiness. B.Tomakehisbusinessknowntomorepeople. C.Togiveadvicetothosewantingtoworkforthemselves. D.Tocomparehavingaregularjobwithstartingabusiness.
如图所示在两个电荷量相等的正点电荷的电场中两电荷连线的中垂面上有一以连线中点O为圆心的圆AB为圆上对称的两点两点电荷连线的延长线上有一点C下列说法正确的是
某同学采用安阻法测电池a的电动势和内阻实验装置如图甲所示实验时多次改变电阻箱R的阻值记录电阻箱的阻值R和电流表的示数I得到R关系如图乙中的图线①所示重复上述实验方法测量电池b的电动势和内阻得到图乙中的图线②． 1由图线①可知电池a的电动势Ea＝V内阻ra＝Ω结果保留两位有效数字． 2若用同一定值电阻先后与电池a及电池b连接则两电池的输出功率PaPb选填“大于”“等于”或“小于”两电池的效率ηaηb选填“大于”“等于”或“小于”．
Capsaicin辣椒素canbeusedasmedicinetohelpreducepain.Itmayseemstrangethatwhatcausespainmightalsomakepaingoaway.Yetit'strue. TiborRohacsisamedicalresearcheratNewJerseyMedicalSchoolinNewark.Herecentlystudiedhowcapsaicinworkstoreducepain.ResearchersalreadyknewthatwhencapsaicinturnsontheTRPV1proteinit'sliketurningonabrightlight.Wheneverthelightisonthepersonexperiencespain.Rohacsandhiscolleaguesthendiscoveredachemicalchainreactionthatlatersilencesthispain.HesaysThelightshinessobrightlythatafterawhilethebulbburnsout.ThentheTRPV1proteincan'tturnbackonagain.Whenthishappensthebrainnolongerfindsoutaboutthefeelingofpain. Thehumanbodyisgoodatrepairingitselfhowever.Eventuallythepainwillfixthispainsystemandcanonceagainsendpainalerts警报tothebrain.HoweveriftheTRPV1proteinisactivated激活oftenthepainsystemmaynotgetachancetorepairitselfintime.Thepersonwillonlyfeeldiscomfortorburningatfirst.Thenheorshewillexperiencerelieffromothertypesofpain.Forexamplepeoplewitharthritisregularlyhavepainintheirfingerskneeshipsorotherjoints.Rubbingacreamcontainingcapsaicinontothepainfulareamayburnatfirst.Afterawhilehowevertheareawillbecomenumb. Rohacswarnsthatcapsaicincreamsdon'tseemtogetdeeplyenoughintotheskintototallyremovepain.Hesaysotherresearchersarecurrentlytestingcapsaicinbandagesorinjections.Theywouldlikelydoabetterjobathaltingpain.Unfortunatelytheytendtohurtalotmorethanacream﹣atleastinthebeginning.Someonewhocantoughoutthediscomforthowevercouldfeelnopaininthefollowingseveralweeksnothours. 32.WhathappenstothepersonwhentheTRPV1proteinisturnedon? A.Heloseshissenses. B.Hesuffersphysicalpains. C.Heslightlysensesdiscomfort. D.Hegetsusedtothefeelingofpain. 33.Whenmaythepainsystemnotrecover? A.WhentheTRPV1proteinburnsout. B.Whenthebraincannotreceivepainalerts. C.WhentheTRPV1proteinisturnedonfrequently. D.Whendifferenttypesofpainoccuratthesametime. 34.Whatistheproblemofcapsaicincreamswhentheyareusedtoreducepain? A.Theyarenotveryeffective. B.Theycauseburnsintheskin. C.Theycausetoomuchdiscomfort. D.Theycanstoppainforjustseveralweeks. 35.Whatdoestheunderlinedwordhaltinginthelastparagraphmean? A.Finding.B.Feeling.C.Hiding.D.Stopping.
如图所示水平面内ab和cd是两条平行放置的足够长直粗糙金属导轨MN和MN是两根用细线连接的金属杆其质量分别为m和2m两杆与导轨的动摩擦因数均为μ．开始时水平外力F作用在杆MN上使两杆以速度υ0水平向右匀速运动．两杆的总电阻为R导轨间距为d整个装置处在磁感应强度为B的匀强磁场中磁场方向与导轨所在平面垂直导轨电阻可忽略重力加速度为g．在t＝0时刻将细线烧断保持外力F不变金属杆和导轨始终接触良好已知在t＝t0时刻后杆MN速度保持不变且在0～t0时间内两杆速度方向始终向右求 10～t0时间内任意时刻两杆的加速度大小之比 2t0时刻两杆各自的速度 30～t0时间内两杆各自的位移．
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