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立体几何:长方体ABCD-A'B'C'D'中,求证A'C'‖平面ABCD 如图所示宇宙飞船发动机内氢气和氧气燃烧生成水的微观过程.下列说法中错误的为什么是水分子是由氢分子,氧分子构成的 已知ABCD-A'B'C'D'为长方体,对角线AC'与平面A’BD相交于点G,则G是三角形A'BD的A 垂心 B 重心 C 外心 D 内心 答案选B 请附上过程!谢谢!已知空间三条直线中，任何两条不共面，且两两垂直，若直 立体几何问题 四棱锥F-ABCD的底面ABCD是菱形四棱锥F-ABCD的底面ABCD是菱形,对角线AC=2,BD=√2,AE,CF都与平面ABCD垂直,AE=2,CF=2.:(1)求二面角B-AF-D的大小（2）求四棱锥E-ABCD与四棱锥F-ABCD公共部分体积安 717.宇宙飞船上的造氧机,其原理是靠电解水产生氧气和氢气吗? 立体几何 已知长方体ABCD-A'B'C'D',求证:AB//平面CDA'B'已知长方体ABCD-A'B'C'D',求证:AB//平面CDA'B'急等!怎么证? 改错There have had great changes in Jiangsu.My bike is the same as you.Please bring the umbrella with you.It is raining outside.I believe there will not be a heavy snow tonight. Is there a shoe store near here?(改为陈述句） 1x2分之1+2x3分之1+3x4分之1+···+x(x+1)分之1=12分之1解方程 请问 ：The man knocked at the door."the door"是宾语吗?这个句子中knocked at the door 是谓语,还是knocked at 是谓语,the door 做宾语 The policeman came up to the lonely house with door ___,____ there..The policeman came up to the lonely house with door ___,____ there for a while and then entered it.a.open; to stand b.opening; stoodc.open; stood d.opened; standing选C 第一个为 是knocked at the door还是knocked on the door 考试一题,there used to be a park,_______? 我填wasn't there,错了,说是didn't there我不知道为什么用didn't,我的思路是there be,反义是be there的格式,哪位高手能解释下为什么是didn't而不是wasn't. there used to be a coffee shop next to you r house,--------?a:wasn't there b:wasn't it ; 为什么不选B? There was a knock at the door.It was the second time someone______me that evening.(2 分)A.interruptedB.had interruptedC.would interruptD.interrupt There___many old and low huoses near our school A.used to have B.used to be 这里为什么选B?used to have 应该怎么用? 2.The new library__B___now was designed by a famous designer from France.A.has been built B.being built为什么不能选 英语翻译还有the one that gives the most water for the least money.怎么译? 已知抛物线经过点A（-1,0）,B(0,-3),C(3,0)三点则抛物线的解析式是 Pair has a beautiful name,the City of （） Paris has a beautiful name, the City of Lights. Do you know what it means? Many beautiful buildingsParis has a beautiful name, the City of Lights. Do you know what it means? Many beautiful buildings 的中文意思 paris is the most beautiful city in the world.改同意句!paris is < > beautiful < > any other city in the world 怎么改? paris is a most beautiful city,where you can see the famous Effel Tower如果题目中没有famous这个形容词,还要the吗?Effel Tower 不是专有名词吗?可是以纯专有名词构成的专有名词就不加the啊。比如说Beijing Universit They sit down and have breakfast.改为一般过去式 they kept the door （ ） the whole nightA opend B opens C opening D open The matter could be______ if they would just sit down and take in peaceA set downB taken apartC sorted outD dug out he sat down on the ________ (sit) nearest to the door. There ___ a museum here. A.used to B.used to do C.used to have D.used to having 衡量信息检索效率的指标有哪些? 信息检索的途径有哪些 I helped my mother ___ the cooking yesterday evening.A.does B.did C.doing 把They had dinner at eight o'clock yesterday evening改成否一般疑特殊疑并对at eight evening 提问请把是什么写清楚 @_@ 否定句呢? There are big desks in the classroom now的意思?