中华民族的象征

大学物理简谐波方程叠加2个谐波y1=5cos(6x-900t),y2=5cos(6x-900t-2),求叠加以后的方程(resultant wave). 一列平面简谐波的表达式为y=0.20cos(100πt+πx),其中x、y的单位为米（m）,t的单位为秒（s）,则该波的传播速度u=___________m/s.设该平面简谐波在x=0处发生了反射,反射端是一个自由端且波的振幅不 Where is the bookstore书店在哪里. 填入适合的单词 where is the bookstore?it's （）the school （）the library.how do the students （）the river? they go on a ropeway.where does the boy live? he lives in a （）far from the city.i'm not （）of walking alone at night.i th 某学校修建了一栋4层数学楼,每层有6间教室,进出这栋大楼共有三道门（两道大小相同的正门和一道侧门）,安全检查中,对这三道门进行了测试,开启一到正门和一道侧门时,2分钟内可以通过400 春天的作文怎么写? bottle是什么意思 fan什么意思 There are some____(bog)over there.Let:s go to see them英语提问 请问：Server address is incorrect or Serveris down for maintenance是什么意思? One-Up-One-Down records maintenance.Maintain records to identify the immediate previous source of food or ingredient received and the immediate subsequent recipient of food or ingredient shipped.请帮我翻译一下吧.全文应该是关于供应商 True it is hard to make accurate predictions.true是做副词用吗? Need to track down time on the machines for a better Total Preventative Maintenance (TPM) system.哪位帮我分析下句子结构,意思我懂,结构不懂. NO one knows for sure,and making predictions is a risky business意思是什么? 为什么可以说乙炔分子中各个原子均处于同一平面内,但不能说乙炔是平面型分子如题. Look!There ________ some chicken in the bowl.A.are B.is C.being D.have Look!there is still some __in the bowlA.porksB.riceC.beefsD.noodles bottle 在pussycat dolls的歌词里发现的 empty bottle是什么意思 funtainer-bottle是什么意思 There is very little petrol left in the tank.The nearest petrol station is a long way away.请问这里的left这里为社么要用过去式呢?有没有相关的例句呢? 翻译成中文This website is temporarily down for the maintenance and will be back soon! website-maintenance是什么意思 bottle 什么意思? 中国古典园林持续发展的自然背景和人文背景 码头上轮船的汽笛声能传播很远的原因码头上轮船的汽笛声能传播很远是因为（ ）A汽笛频率高 B汽笛声传播快 C汽笛声音色好 D汽笛声的响度大铁路旁,路检工人用铁锤敲打铁轨和铁轨上的部 站在离码头不同的距离的地方听码头上轮船的汽笛声,感觉到汽笛声不同的是? perhaps maybe区别不要复制这个答案：perhaps与maybe perhaps意为“也许”，“可能”，是副词，含有“也许是如此，也许不是如此”的意味，如：But perhaps they don't know that yet.但是他们可能还不知道 翻译:Server Maintenance maybe和perhaps有什么区别?请说得详细一些,最好举例. maybe 和perhaps的区别 servers are currently under maintenance什么意思