<例句>
The plane,which is usually very punctual,was late today.
这班飞机通常很准时，不过今天却晚点了。
<语法分析>
这个句子为典型的非限制性定语从句。可以看出这类从句对所修饰的都有词没有限制词义的作用，只是一些补充性的说明，而且通常都有逗号把它和句子的其他部分隔开，多译成一个并列句。把从句拿掉以
后，对句子的剩下部分没有太大的影响。我们把which is usually very punctual拿掉以后，句子就变成了The plane was late today.意思仍很完整，合乎语法。需要留意的是，在这类从句中不可用关系
代词that和关系副词why，也不可以把其他的关系副词给省略掉，此类从句多用于书面语中。
<触类旁通>
(1)Tom,who had been driving all night,suggested stopping at the next town.
汤姆开了一夜的车，建议在下一个镇子上停下来。
语法分析：简单、合乎规范的句子。
(2)The buses,most of which were already full,were surrounded by old men.
公共汽车大部分都已载满了乘客，周围是一群老人。
语法分析：在非限制性定语从句中，which和whom常可以与of或其他介词连用。
(3)I drank beer,which made me fat.
我喝啤酒，这使我的身体发胖了。
语法分析：which不代表一个名词，而代表了前面句子的全部或者部分意思。
(4)Such money as he earned was spent on his girl friend.
他挣的那点钱都花在了他女朋友身上。
语法分析：as用作关系代词，引导定语从句，主要和such连用，也可单独引导一个从句。
(5)Surely there isn't a teacher but faces this problem.
可以确定，凡是老师都会面临这个问题。
语法分析：but作为关系代词引导定语从句。
(6)I've set a plan whereby you can spread the cost over a period.
我定了一个办法，你可以照此分期付款。
语法分析：whereby引导一个定语从句，其意思等于by which，类似用法还有wherein和whereupon等。
<巩固练习>
(1)She returned with _____ provisions _____ were needed.
(2)He hoped to give me a chance _____ nobody else ever had.
(3)There is no tree _____ bears some fruits.
(4)This is Mr.Smith,_____ I was working,was very generous.
(5)She changed her mind,_____ made me very angry.
(6)He is a teacher,_____ is clear from his manner.
<参考答案>
(1)such...as (2)such as (3)out (4)for whom (5)which (6)as
