4)若主句中有疑问代词who, which 为了避免重复, 关系代词不要再用who, which.

  Which of the books that were borrowed fromhim is the best?

  Who is the person that talked with your father just now?

2． which 引导非限定性定语从句有时也可代替主句整句话的意思，表示上述情况。

e.g. Some of the roads were flooded, which made our journey more difficult.

The sun gives off light and warmth, which makes it possible for plants to grow.

3. as 引导的从句可以放在句首, as 本身有“正如…..正象…”. 一类的含义. 与之连用的词有know, see, expect, announce, point out等. 记住以下结构：     

e.g.  as is well known                                                              as has been said before                                                

as was expected                                                              as we all can see                                                               as may be imagined                                                      as has been already pointed out

                 e.g. As is known to all, the compass was first made in China.

                    John got beaten in the game, as had been expected.

                    As has been said above, grammar is a set of dead rules.

      4. 在the same…as…, such…as…, so…as…中as引导的是限制性定语从句.

e.g. There isn’t so much noise in the country as in big cities.

               I could only read such stories as had been written in simple English.

   I have bought the same dress as she is wearing.

      5. 介词﹢关系代词引导的定语从句,关键是判断介词的选择（介词只与which 和 whom 连用，which表示物，whom表示人）。

方法一：部分介词选择取决于定语从句中的动词，看从句谓语部分缺少什么介词(动词的固定搭配)

        e.g. The woman to whom my brother spoke just now is my teacher.

            Jeanne was her old friend, from whom she borrowed a necklace.

           方法二：部分介词取决于被定语从句修饰的先行词，将先行词带入从句，看选则哪个介词

       e.g. I’ll never forget the day on which I joined the League.

          The Second World War during which millions of people were killed ended in 1945.

He built a telescope through which he could study the skies.

方法三：可以通过整个句子整体含义来判断，将先行词带入从句中（结合生活实际）

     e.g. His glasses, without which he was like a blind man, fell to the ground and broke its leg.

        There are two thousand students in hour school, of whom two thirds are boys.

     特别注意1：有些介词只能放在关系代词前面，而有些绝不能放在关系代词前面

     e.g.           e.g. His little brother whom his mother asked him to look after is very naughty.        （此时after不能放到whom 前面，因为look after是固定词组，拆开后就会失去它         想表达的意思或产生歧意。）

       e.g. Do you know who lives in the building in front of which there is a well?

                        Please pass me the dictionary the cover of which is black.

         （此时介词必须放在which前，否则句意不通）

      特别注意2：有些介词+关系代词的情况可以和关系副词互换

       e.g. I often thought of my childhood in which/when I lived on a farm.

          Is it the faction in which/where “Red Flag” cars are produced?

          Is that the reason for which/why you were late.

    6. 特例：极少数定语从句中出现了介词+关系副词from +where

        e.g. China is the birthplace of kites, from where kite flying spread to Japan, Korea, Thailand and India.                 

    7. 易混考点：

v   先行词是表示地点的词或短语，关系词不一定都是where或介词+which, 还是要分析它在从句中担当的语法成分

e.g. The wolves hid themselves in the places that/which couldn’t be found.                                                             

v   先行词是表示时间的词或短语，关系词不一定都是when, 还是要分析它在从句中担当的语法成分

e.g. The manager had to go to Beijing on June 23, which/that happened to be his only son’s birthday.                           

v   先行词是reason,关系词不一定都用why

          e.g. This is the reason that/which he has always been eager to know for these years.

              Is this the only reason that makes you unhappy.                                                                            

v   先行词为the way,表途径、方式时，关系词that(that 可省略），in which  

皆可

                  I don’t like the way (that)/in which you speak to her.

                                                                                  ------ created by  Meg