在英语中什么时候要用be动词（is,am,are）

现在时Iam,youare,heis,weare,youare,theyare（缩略式I'm,you're,he's,we're,you're,they're）,（否定缩略式I'mnot,isn't,aren't）,过去时Iwas,youwere,hewas,wewere,youwere,theywere（过去时否定缩略式wasn't,weren't）,过去分词been,现在分词being英语的“be”是个特别动词；有些语言，“Be”除了原形的“be”之外，还有另外七种形式：am,is,are,been,being,was,were.在句子中，“be”可以是主动词(ThePrincipalVerb)或助动词(TheAuxiliaryVerb).【当主动词时，“be”在性质上属于接系动词(TheLinkingVerb),后面要有名词、形容词、地方副词或短语作补足语(TheComplement)。例如：1.Themanisascienceteacher.2.Mary'snewdressesarecolourful.3.Ihavebeentherebefore.4.Motherisinthekitchennow.【这四个都是陈述句，可以变成疑问句，方法简单，把主语和“be”或助动词对换位置即可：5.Isthemanascienceteacher?6.AreMary'snewdressescolourful?7.HaveIbeentherebefore?8.Ismotherinthekitchennow?【当“be”要在祈使句中出现时，它必须借重助动词“do”或“don't”之助，如：9.Don'tbesilly!10.Dobeobedient!11.Don'tbeafool!【“Be”有两种缩写法，如下：12.He'snot...../Heisn't....13.You'renot...../Youaren't...【但“am+not”的缩写法只有一个：14.I'mnot.有人用“ain't”,但这并不是标准英语。谈过了“be”作主动词的功能，现在看看“be”作助动词时，有些什么用法：【1.】“Be+现在分词”以组成进行式时态(ContinuousTenses)，如：15.Tony'smaidiswashinghisnewcar.16.Thechildrenareplayinginthefield.17.SamuelwaseatingwhenIcamein.18.Wehavebeenlivingheresince1959.【2.】“Be+过去分词”以组成被动语态(ThePassiveVoice),如：19.Hermoneyinthedrawerwasstolen.20.Anumberofgoodjobsaretakenupbyforeigners.21.DavidstudiedinTaiwanbuthasbeentrainedasalanguagelecturerinAmerica.22.CanallthewonderfulbirdsbefoundinourBirdPark?23.Thedisobedientboywastoldtostandout-sidetheclassroom.24.Stepsarebeingtakentoreducetrafficcon-gestionduringpeakhours.25.Dishoneststudentswillbeimmediatelydealtwith.