向老师请教：to be taught在下句中是否是不定式的被动语态做表语?为什么不直接用was taught呢?

一、被动语态的构成形式 　　1 被动语态的基本时态变化 　　被动语态通常为十种时态的被动形式, 被动语态由be＋过去分词构成,be随时态的变化而变化.以do为例,各种时态的被动语态形式为： 　　1) am/is/are +done 一般现在时 　　例Visitors are requested not to touch the exhibits 2） has /have been done 现在完成时 　　例All the preparations for the task have been pleted, and we're ready to start 　　3） am/is /are being done 现在进行时 　　例A new cinema is being built here． 　　4） was/were done 一般过去时 　　例I was given ten minutes to decide whether I should reject the offer 　　5） had been done 过去完成时 　　例 By the end of last year, another new gymnasium had been pleted in Beijing 　　6） was/were being done 过去进行时 　　例A meeting was being held when I was there 　　7） shall/will be done 一般将来时 　　例Hundreds of jobs will be lost if the factory closes 　　8） should/would be done 过去将来时 　　例The news would be sent to the soldier's mother as soon as it arrived 　　9） shall/will have been done 将来完成时（少用） 　　例The project will have been pleted before July 　　10） should/would have been done 过去将来完成时（少用） 　　例He told me that his new clothes would have been made very soon 　　2 被动语态的特殊结构形式 　　1)带情态动词的被动结构.其形式为：情态动词＋be＋过去分词. 　　例The baby should be taken good care of by the baby-sitter 　　2) 有些动词可以有两个宾语,在用于被动结构时,可以把主动结构中的一个宾语变为主语,另一宾语仍然保留在谓语后面.通常变为主语的是间接宾语. 　　例His mother gave him a present for his birthday 可改为 He was given a present by his mother for his birthday 　　3) 当“动词+宾语+宾语补足语”结构变为被动语态时,将宾语变为被动结构中的主语,其余不动. 　　例Someone caught the boy smoking a cigarette 可改为The boy was caught smoking a cigarette 　　4）在使役动词have, make, get以及感官动词see, watch, notice, hear, feel, observe等后面不定式作宾语补语时,在主动结构中不定式to要省略,但变为被动结构时,要加to. 　　例Someone saw a stranger walk into the building 可改为A stranger was seen to walk into the building 　　5) 有些相当于及物动词的动词词组,如“动词＋介词”,“动词＋副词”等,也可以用于被动结构,但要把它们看作一个整体,不能分开.其中的介词或副词也不能省略. 　　例The meeting is to be put off till Friday 　　3 非谓语动词的被动语态 　　v+ing 形式及不定式 to do 也有被动语态 . 　　例I don't like being laughed at in the public 　　二、 如何使用被动语态 　　学习被动语态时,不仅要知道被动语态的各种语法结构,还要知道在哪些情况中使用被动语态. 　　1 讲话者不知道动作的执行者或不必说出动作的执行者 . 　　例 My bike was stolen last night 　　2 借助被动的动作突出动作的执行者. 　　例 I was given ten minutes to decide whether I should accept the offer 　　3 为了更好地安排句子. 　　例The well-known person got on the bus and was immediately recognized by people （一个主语就够了）
三、 It is said that+从句及其他类似句型 　　一些表示“据说”或“相信”的动词如believe, consider, expect, report, say, suppose, think等可以用于句型“It＋be＋过去分词＋that从句”或“主语＋be＋过去分词＋to do sth”.有： 　　It is said that… 据说,It is reported that…据报道,It is believed that…大家相信,It is hoped that…大家希望,It is well known that…众所周知,It is thought that…大家认为,It is suggested that…据建议.　 　　例It is said that the boy has passed the national exam （＝The boy is said to have passed the national exam ） 　　四、谓语动词的主动形式表示被动意义 　　1英语中有很多动词如 break,catch,clean,drive,lock,open,sell,read,write,wash等,当它们被用作不及物动词来描述主语特征时,常用其主动形式 表达被动意义,主语通常是物. 　　例 This kind of cloth washes well 　　注意：主动语态表被动强调的是主语的特征,而被动语态则强调外界作用造成的影响. 　　试比较：The door won't lock． （指门本身有毛病） 　　The door won't be locked． （指不会有人来锁门, 指“门没有锁”是人的原因） 　　2 表示“发生、进行”的不及物动词和短语,如：happen, last, take place, break out, e out, e about, e true, run out, give out, turn out等以主动形式表示被动意义. 　　例 How do the newspapers e out? 这些报纸是如何引出来的呢? 　　3 系动词没有被动形式, 但有些表示感受、感官的连系动词feel, sound, taste, book, feel等在主系表结构中常以主动形式表示被动意义. 　　　 例Your reason sounds reasonable 　　五、非谓语动词的主动形式表被动意义 　　在某些句型中可用动名词和不定式的主动形式表被动意义 . 　　1． 在need,want,require, bear等词的后面,动名词用主动形式表示被动意义,其含义相当于动词不定式的被动形式. 　　例The house needs repairing（to be repaired）．这房子需要修理. 　　2． 形容词worth后面跟动名词的主动形式表示被动含义,但不能跟动词不定式；而worthy后面跟动词不定式的被动形式. 　　例The picture-book is well worth reading．（＝The picture-book is very worthy to be read．） 　　3 动词不定式在名词后面作定语,不定式和名词之间有动宾关系时,又和句中另一名词或代词构成主谓关系, 不定式的主动形式表示被动含义. 　　例 I have a lot of things to do this afternoon． 　　试比较：I’ll go to the post office Do you have a letter to be posted? 　　4 在某些“形容词＋不定式”做表语或宾语补足语的结构中,句子的主语或宾语又是动词不定式的逻辑宾语时,这时常用不定式的主动形式表达被动意义.这些形容词有nice,easy,fit,hard,difficult,important,impossible,pleasant,interesting等. 　　例This problem is difficult to work out （可看作to work out省略了for me） 　　5． 在too… to…结构中,不定式前面可加逻辑主语,所以应用主动形式表示被动意义. 　　例This book is too expensive to buy 　　6 在there be…句型中,当动词不定式修饰名词作定语时,不定式用主动式作定语,重点在人,用被动形式作定语,重点在物.