It's a pity..的疑问It's a pity he couldn't visit Mary.这是个定语从句吧?I could drive a car by the time I was sixteen.这是什么从句?

It's a pity..的疑问It's a pity he couldn't visit Mary.这是个定语从句吧?I could drive a car by the time I was sixteen.这是什么从句?
It's a pity..的疑问
It's a pity he couldn't visit Mary.这是个定语从句吧?I could drive a car by the time I was sixteen.这是什么从句?

It's a pity..的疑问It's a pity he couldn't visit Mary.这是个定语从句吧?I could drive a car by the time I was sixteen.这是什么从句?
一、“it is + 形容词表语 + 从句”叫做主语从句,其中 1.结构说明 * it 是形式主语,* 从句是真实主语.2.该结构的作用 如果不采取形式主语的办法,这个句子应该是如下的结构：he couldn't visit Mary is a pity.很明显,主语部分是个较长的句子,而表语却只有一个形容词,整个句子显得头重脚轻.为了避免这种头重脚轻得凝重句式,于是就把做主语的从句放在句尾,主语空出来的位置由形式代词 it 来充当.英语里,如果主语由较长的不定式短语、动名词短语或句子充当的时候,常常会出现这种“垂帘听政”的句式结构,而帝位则由“傀儡皇帝”it“听政”.例如：不定式：It is difficult to study English Grammar.学习英语语法很难.动名词：It is no good eating more.多吃食没有好处的.从句：It's a pity that he couldn't visit Mary.二、I could drive a car by the time I was sixteen 中的by the time I was sixtteen 可以作如下几种理1.最易于理解的是把 by the time 看成一个复合的引导时间状语的连词,如果这样,它就是时间状语从句； 2.比较复杂的办法则是把 by the time 和 I was sixtteen 分开来分析：* by the time 介词短语作时间状语,意思是“到那时为止” 或者“在那以前”； * I was sixtteen 是省略关系词 when 或 at which 的定语从句,即“（在）我16岁的时候（以前）”.英语语法里常把“the + 表示时间的名词”规定为复合连词,用来引导时间状语从句,如：the moment 就在...那一刻 the time 就在...那个时刻 the day 就在...那一天 the year 就在...那一年 g