定語從句是由關系代詞或關系副詞引導的從句

1、定語從句是由關系代詞或關系副詞引導的從句，其作用是作定語修飾主句的某個名詞性成分，相當于形容詞，所以又稱為形容詞性從句，一般跟在它所修飾的先行詞后面。在復合句中，修飾某一名詞或代詞叫做定語從句。 關系詞 引導定語從句的關聯詞稱為關系詞，關系詞有關系代詞和關系副詞。關系代詞有that, which, who, whom, whose, as等，絕對沒有what；關系副詞有where, when, why等。關系詞常有3個作用： 連接作用，引導定語從句。 代替主句中的先行詞，甚至可能是主句中的一部分或者整個主句。 在定語從句中充當一句子成分。 注：關系代詞有主語、賓語之分。一般whom作為賓語。關

2、系代詞在從句中作主語，賓語，表語，定語等，關系副詞在從句中作地點狀語，時間狀語，原因狀語等。 定語 定語用來限定、修飾名詞或代詞的，是對名詞或代詞起修飾、限定作用的詞、短語（動詞不定式短語、動名詞短語和分詞短語）或句子，漢語中常用的表示。主要由形容詞擔任，此外，名詞，代詞，數詞，分詞，副詞，不定式以及介詞短語也可以來擔任，也可以由一個句子來擔任。單詞作定語時通常放在它所修飾的詞之前，作前置定語。短語和從句作定語時則放在所修飾的詞之后，作后置定語。 先行詞 被定語從句修飾的名詞、代詞稱為先行詞。 關系代詞引導的定語從句舉例 關系代詞所代替的先行詞是人或物的名詞或代詞，并在從句中充當主語、賓語、定

3、語等成分。關系代詞在定語從句中作主語時，從句謂語動詞的人稱和數要和先行詞保持一致。 who, whom, that 這些詞代替的先行詞是人的名詞或代詞，who做主語指人，whom作賓語指人，that既可作主語又可作賓語（作賓語可以省略），可以指人也可以指物。在從句中所起作用如下： (1) Is he the man who/that wants to see you? 他就是想見你的人嗎？（who/that在從句中作主語） (2) He is the man whom/ that I saw yesterday. 他就是我昨天見的那個人。（whom/that在從句中作賓語） Whose 用來指

4、人或物 (只用作定語, 若指物，它還可以同of which互換，指人的時候也可以用of whom 代替） (1) They rushed over to help the man whose car had broken down. 那人車壞了，大家都跑過去幫忙。 (2) Please pass me the book whose (of which) color is green. 請遞給我那本綠皮的書。 which, that 它們所代替的先行詞是事物的名詞或代詞，在從句中可作主語、賓語等，作賓語時可以省略，例如： (1) A prosperity which / that had nev

5、er been seen before appears in the countryside. 農村出現了前所未有的繁榮。（which / that在句中作主語） (2) The package (which / that) you are carrying is about to come unwrapped. 你拿那個包裹快要散開了。(which / that在句中作賓語） 4、 as as 可以做主語，也可以作賓語，作賓語時可以省略，指人或者物。常與such as,the same as等短語連用。 限定性定語從句 關系代詞 關系代詞：在句中作主語、賓語或定語 1. that既可代表事物

6、也可代表人，which代表事物；它們在從句中作主語或賓語，that在從句中作賓語時?？墒÷躁P系詞，which在從句中作賓語也可以省略。 eg：This is the book （which）you want. 2. 如果which在從句中作“不及物動詞介詞”的介詞的賓語，注意介詞不要丟掉，而且介詞總是放在關系代詞which的前邊，但有的則放在它原來的位置 3. 代表物時多用which，但在下列情況中用that而不用which： a)先行詞是anything, everything, nothing , none等不定代詞時； b)先行詞由every, any, all, some, no, l

7、ittle, few, much等修飾時，這時的that常被省略； c)先行詞前有序數詞或被形容詞最高級修飾時； d)先行詞中既有人又有物時； e)整個句中前面已有which，who,that時； f)當先行詞為物并作表語時； g)先行詞為one時； h)先行詞同時又被the only,the very,the same修飾時； 4. who和whom引導的從句用來修飾人，分別作從句中的主語和賓語，whom作賓語時，要注意它可以作動詞的賓語也可以作介詞的賓語 5. whose是關系代詞，修飾名詞作定語，相當于所修飾成分的前置所有格.它引導的從句可以修飾人和物, 當它引導的從句修飾物體時, 可以

8、與 of which 調換,表達的意思一樣。 關系副詞 關系副詞：在句中作狀語 關系副詞=介詞+關系代詞 why=for which where=in/ at/ on/ . which (介詞同先行詞搭配) when=during/ on/ in/ . which (介詞同先行詞搭配) 1. where是關系副詞，用來表示地點的定語從句。 2. when引導定語從句表示時間注值得一提的是，表示時間“time一詞的定語從句只用when引導，有時不用任何關系代詞，當然也不用that引導。 By the time you arrived in London, we had stayed there

9、for two weeks. 到你到達倫敦的時候，我們在那里已經待了兩個星期。 I still remember the first time I met her. 我仍然記得我第一次見到她。 Each time he goes to business trip, he brings a lot of living necessities, such as towels, soap, toothbrush etc。 每一次他去出差，他帶來了生活必需品，如毛巾，肥皂，牙刷等，很多。 3. 當從句的邏輯主語是some, any, no, somebody, anybody, nobody, som

10、ething, anything, everything或nothing時，常用there is來引導 There is somebody here who wants to speak to you. 這里有人要和你說話。 非限制性定語從句非限制性定語從句的作用是對所修飾的成分作進一步說明，通常是引導詞和先行詞之間用逗號隔開，將從句拿掉后其他部分仍可成立 1. which引導的非限定性定語從句作用是說明前面整個句子的情況或主句的某一部分 2.當先行詞是專有名詞、物主代詞或指示代詞所修飾時，其后的定語從句通常是非限制性的，例如： Charles Smith, who was my former

11、 teacher, retired last year. 查理史密斯去年退休了，他曾經是我的老師。 My house, which I bought last year, has got a lovely garden. 我去年買的的那幢房子帶著個漂亮的花園。 This novel, which I have read three times, is very touching. 這本小說很動人，我已經讀了三遍。 3.非限定性定語從句可將整個主句作為先行詞, 對其進行修飾, 這時從句謂語動詞要用第三人稱單數，例如： He seems not to have grasped what I mea

12、nt, which greatly upsets me. 他似乎沒抓住我的意思，這使我心煩。 Liquid water changes to vapor, which is called evaporation. 液態(tài)水變?yōu)檎羝?，這就叫做蒸發(fā)。 4. 有時as也可用作關系代詞 5. 在非限定性定語從句中，不能用關系副詞why和關系代詞that，而用who, whom代表人，用which,whose代表事物，如果需要用why，可用for which代替.；p.s: which引導的非限制性定語從句其后不可省略成分，as可以 關系代詞引導的定語從句 who指人在從句中做主語 (1) The boy

13、s who are playing football are from Class One. 在踢足球的男孩們是一班的. (2) Yesterday I helped an old man who lost his way. 昨天，我?guī)椭艘粋€迷路的老人. whom指人,定語從句中充當賓語，常省略。 （注：who和whom已無太大區(qū)別，基本可以通用。區(qū)別是who可以做主語而whom不可以，whom前可以加介詞如to whom，但是who不可以） (1) Mr. Liu is the person (whom) you talked with on the bus. 劉先生就是在公交車上和你聊天

14、的那個人. (2) Mr. Ling is just the boy(whom)I want to see. 凌先生恰巧就是我想見的那個男孩. (3) The man who/whom you met just now is my friend. 你剛剛見到的那個人就是我的朋友. 注意：關系代詞whom在口語和非正式語體中常用who代替，可省略。 如果在從句中做賓語,就用whom或who.比如: He is the man whom/who I talk to. 他就是那個和我聊天的男人. 如果是在從句中作主語就只能用who.比如: He is the man who has an Engli

15、sh book. 他就是那個有英語書的男人. whose通常指人也可指物,在定語從句中做定語。 He has a friend whose father is a doctor. 他有一個朋友的父親是醫(yī)生. (2) I once lived in a house whose roof has fallen in. whose指物時通常以以下結構來代替 (3) The classroom whose door is broken will soon be repaired. 那個門被打破的教室不久會被修復。 (4) The classroom the door of which is broke

16、n will soon be repaired. 課堂門，被打破會不久被修復。 (5) Do you like the book whose color is yellow? 你喜歡顏色是黃色的書嗎? (6) Do you like the book the color of which is yellow? 你喜歡的書的顏色，是黃色嗎? which指物 在定語從句中做主語，表語，定語或者賓語，做賓語時可省略。 (1) Football is a game which is liked by most boys. 足球是大多數男孩都喜歡的游戲. (2) This is the pen (whi

17、ch) he bought yesterday. 這是他昨天剛買的鋼筆. that指人時,相當于who或者whom；指物時，相當于which。在定語從句中做主語,表語或者賓語，做賓語時可省略。 5) The number of the people that/who come to visit the city each year rises one million. 數目的人民那個/誰來城市觀光每年上升之一個百萬 (6) Where is the man that/whom I saw this morning?那個男人在哪里/我看見誰了今天早上? 關系副詞引導的定語從句 when指時間,在

18、定語從句中做時間狀語也可做連接詞用 (1) I still remember the day when I first came to the school. (2) The time when we got together finally came. where指地點,在定語從句中做地點狀語 (1) Shanghai is the city where I was born. (2) The house where I lived ten years ago has been pulled down. why指原因,在定語從句中做原因狀語 (1) Please tell me the re

19、ason why you missed the plane. (2) I dont know the reason why he looks unhappy today. 注意：關系副詞引導的從句可以由“介詞+關系代詞”引導的從句替換 (1) The reason why/ for which he refused the invitation is not clear, (2) From the year when/in which he was going to school he began to know what he wanted when he grew up. 介詞和關系代詞

20、1）介詞后面的關系代詞不能省略。 2）that前不能有介詞。 3） 某些在從句中充當時間，地點或原因狀語的介詞+關系詞結構可以同關系副詞when ,where和why 互換。 This is the house in which I lived two years ago. This is the house where I lived two years ago. Do you remember the day on which you joined our club? Do you remember the day when you joined our club? This is the

21、 reason why he came late. This is the reason for which he came late. 介詞+關系代詞引導的定語從句關系代詞在定語從句中做介詞賓語時 從句常由介詞+關系代詞引導 當介詞放在關系代詞前面時，關系代詞只能用which/whom即“介詞+which/whom且不能省略。但當介詞位于末尾時可用that/which/who/whom.作介詞的賓語，且可以省略。例如： (1) The school (that/which) he once studied in is very famous.that/which可以省略 = The scho

22、ol in which he once studied is very famous.which”不可省略 (2) Tomorrow I will bring here a magazine (that/which) you asked for. = Tomorrow I will bring here a magazine for which you asked. (3) Well go to hear the famous singer (whom/that/who) we have often talked about. = Well go to hear the famous sing

23、er about whom we have often talked. 注意： 1. 含有介詞的動詞短語一般不拆開使用， 如：look for, look after, take care of等 T This is the watch which/that I am looking for. (T正確) F This is the watch for which I am looking. (F錯誤) 2. 若介詞放在關系代詞前，關系代詞指人時用whom，不可用who或者that；指物時用which，不能用that；關系代詞是所有格時用whose (1) The man with whom

24、you talked is my friend. (T) The man with that you talked is my friend. (F) (2) The plane in which we flew to Canada is very comfortable. (T) The plane in that we flew in to Canada is very comfortable. (F) 3. “介詞+關系代詞”前可有some, any, none, both, all, neither, most, each, few等代詞、數詞或者名詞。 (1) He loved hi

25、s parents deeply, both of whom are very kind to him. (2) In the basket there are quite many apples, some of which have gone bad. (3) There are forty students in our class in all, most of whom are from big cities. (4）The boat, the name of which is Topsail, is famous. (5）I bought many books yesterday,

26、 three of which are written by Lu Xun. 關系代詞 關系代詞（一般情況下）that 可用在從句做主語，謂動詞的賓語，但是不能做介詞的賓語。which指物，在從句中作主語，謂語或賓語；who在從句中作主語；whom在從句中作賓語；where在從句中修飾表地點的名詞，做地點狀語；when在從句中通常修飾表時間的名詞，做時間狀語；why在從句中做原因狀語，先行詞通常是reason 有時why也可用for+which代替。 例：A doctor is a person who looks after peoples health. 主語 謂語 先行詞 定語從句修飾先

27、行詞 判斷介詞和關系代詞 方法一： 用關系代詞，還是關系副詞完全取決于從句中的謂語動詞。不及物動詞后面無賓語，就必須要求用關系副詞或者是介詞加關系代詞；而及物動詞后接賓語，則要求用關系代詞。 例如： This is the mountain village where I stayed last year. Ill never forget the days when I worked together with you. 判斷改錯（注：先顯示題，再顯示答案，橫線；用不同的顏色表示出。） （錯） This is the mountain village where I visited last

28、 year. （錯） I will never forget the days when I spent in the countryside. （對） This is the mountain village (which) I visited last year. （對） Ill never forget the days (which) I spent in the countryside. 習慣上總把表地點或時間的名詞與關系副詞 where, when聯系在一起。此兩題錯在關系詞的誤用上。 方法二： 準確判斷先行詞在定語從句中的成分(主、謂、賓、定、狀)，也能正確選擇出關系代詞/關系副

29、詞。 例1. Is this museum _ you visited a few days ago? A. whereB. thatC. on whichD. the one 例2. Is this the museum _ the exhibition was held? A. whereB. thatC. on whichD. the one 答案：例1 D，例2 A 例1變?yōu)榭隙ň洌?This museum is _ you visited a few days ago. 例2變?yōu)榭隙ň洌?This is the museum _ the exhibition was held. 在句

30、1中，is后應跟表語，只有the one可以，而后面的you visited a few days ago則做one的定語從句,而句2中, 主、謂、賓俱全，從句部分為句子的狀語表地點，既可用副詞where，又因 in the museum詞組，可用介詞in + which 引導地點狀語。而此題中，介詞on 用的不對，所以選A。 關系詞的選擇依據在從句中所做的成分，先行詞在從句中做主、定、賓語時，選擇關系代詞 (who, whom, that, which, whose)；先行詞在從句中做狀語時，應選擇關系副詞 ( where 地點狀語，when 時間狀語，why 原因狀語) 。 先行詞和關系詞

31、 1)Whoever spits in public will be punished here.(Whoever 可以用 anyone who 代替) 2)The parents will use what they have to send their son to technical school. (what 可以用all that代替) 。 但這兩句句子已經不是定語從句了，是名詞性從句。因為定語從句一定要有先行詞，而名詞性從句沒有。將“Whoever”、“what”分別用“Anyone who”、“all that”代替后，才是定語從句，先行詞分別是“Anyone”、“all”。 a

32、s,which引導的非限制性定語從句 由as, which 引導的非限定性定語從句，as和which可代整個主句，相當于and this或and that。As一般放在句首，which在句中。 As we know, smoking is harmful to ones health. The sun heats the earth, which is very important to us. 典型例題 1）Alice received an invitation from her boss, _came as a surprise. A. itB. thatC. whichD. he 答案

33、C。此為非限定性從句，不能用 that修飾，而用which.，it 和he 都使后句成為句子，兩個獨立的句子不能單以逗號連接。況且選he句意不通。 2）The weather turned out to be very good, _ was more than we could expect. A. whatB. whichC. thatD. it 答案B。 which可代替句子，用于非限定性定語從句，而what不可。That 不能用于非限定性定語從句，it不為連詞，使由逗號連接的兩個句子并在一起在英語語法上行不通。 3）It rained hard yesterday, _ prevent

34、ed me from going to the park. A. thatB. whichC. asD. it 答案B。 as 和which在引導非限制性定語從句時，這兩個關系代詞都指主句所表達的整個意思，且在定語從句中都可以作主語和賓語。但不同之處主要有兩點： (1） as 引導的定語從句可置于句首，而which不可。 (2） as 代表前面的整個主句并在從句中作主語時，從句中的謂語必須是系動詞；若為行為動詞，則從句中的關系代詞只能用which.。在本題中，prevent由于是行為動詞，所以正確選項應為B。 As 的用法例 例1. the same as；suchas 中的as 是一種固定結

35、構, 和一樣。 I have got into the same trouble as he (has). 例2. as可引導非限制性從句，常帶有正如。 As we know, smoking is harmful to ones health. As is known, smoking is harmful to ones health. As是關系代詞。例1中的as作know的賓語； 例2中，它充當從句的主語，謂語動詞know要用被動式。 一、“as / which” 特殊定語從句的先行成分 1. 形容詞或形容詞短語作先行成分, 具有形容詞意義的介詞短語也可以充當先行成分，如： My gr

36、andmothers house was always of great importance to me, as my own is. 在一定的語言環(huán)境里，有些名詞可以具有形容詞的性質。這些名詞主要是那些表示人的身份、職業(yè)、狀態(tài)的名詞。值得一提的是，在這些具有形容詞性質的名詞之后，引導定語從句的關系代詞不能用who / whom. 2. 動詞短語先行成分。 這種動詞短語既可是限定形式也可是非限定形式。如果是動態(tài)動詞短語，它們在從句中就一般有限定或非限定形式的替代動詞do和as / which一起代替。do可以出現，也可以不出現，但不能用其它動詞代替。 3. 句子作先行成分。 這句子可以是整個

37、主句也可以只是主句中的一個從句。有時是連續(xù)幾個句子，有時甚至可以是一個完整的故事。 二、“as/which”特殊定語從句在句中的位置 由于先行成分的構成成分不同，“as/which”特殊定語從句在句中的位置有以下幾種情況： 1. 形容詞做先行成分時： 形容詞或形容詞短語（含具有形容詞性質的名詞）作先行成分，“as / which”特殊定語從句置于先行成分之后。 2. 動詞短語作先行成分時： 動詞短語作先行成分時，“as / which”特殊定語從句置于先行成分之后。但是，當從句中含有表示主觀意志的插入成分時，“as”特殊定語從句可以移至句子之首。 3. 句子作先行成分時： “as”特殊定語從句

38、的位置較靈活，可以置于先行成分之前、之中或之后。但如果先行成分是直接引語，“as”特殊定語從句多在先行成分之前。如果先行成分是否定句，“as”特殊定語從句與否定詞的相對位置不同可以使它產生不同的意義。由于“as”特殊定語從句具有這一特點，所以有時它的位置不能隨便移動。在非正式的文體里，“which”特殊定語從句可以出現在先行成分之中。 三、“as/which”特殊定語從句的語義功能 一般說來，as與which的語義功能相同，可以相互替換。但先行成分為句子時，它們的語義功能則有差異。 1. 表示結果 表示結果的特殊定語從句與其先行成分之間存在著一定的因果關系，從句中往往使用有結果意義的詞，如動詞

39、result, make, enable, cause和形容詞interesting, surprising, delightful, disgraceful等。 2. 表示評注 表示評注的特殊定語從句對其先行成分所述事實的正確性有肯定的傾向，它通常與那些表示客觀事實，普遍真理或某種習性的先行成分連用；從句中則常用一些表示“合乎自然規(guī)律”、“眾所周知”或“經常發(fā)生”等意義的詞語，如natural, known to all, usual等。 3. 有無狀語意義 “as”特殊定語從句具有狀語意義（主要是方式狀語意義），而“which”特殊定語從句則無狀語意義?！癮s”特殊定語從句的狀語意義要求它

40、在語義上與其先行成分的語義保持一致，“which”特殊定語從句則不受這種限制。 四、關系代詞as與which的句法功能 1. as / which 在特殊定語從句中作主語。 as作主語時，謂語動詞常為連系動詞（主要是be, seem），主語補語為usual、 a rule、 a matter of fact等時，系動詞be習慣經常省略。行為動詞作“as”特殊定語從句的謂語時一般用于被動語態(tài)（其中助動詞be常略），不及物的行為動詞在“as”特殊定語從句中作謂語的極少，常見的有happen一詞。如： Freddie, as might be expected, was attending the

41、conference. Which作主語時，謂語動詞不限，主動被動皆可，只是謂語動詞為被動語態(tài)時助動詞be省略。 2. as和which都可以在特殊定語從句中賓語。 3. as和 which在特殊定語從句中作補語。如： We thought him a gentleman, as/which he could never be. “as”特殊定語從句中可以主謂倒裝，“which”從句中則不能主謂倒裝。 如果先行成分不是主語補語或賓語補語，關系代詞用which而不用as。如： He talked like a native, which/as he hardly was. 4. which在特殊

42、從定語句中作定語。 which可以在特殊定語從句中作定語，修飾fact, matter, thing 等名詞。這些名詞代表先行成分表達的意義，有時將其略去句義仍然完整。as不能作定語。如： I was told to go not by train but bus, which advice I followed. 關系代詞that 的用法 (1)不用that的情況 (a) 在引導非限定性定語從句時。 (錯)The tree, that is four hundred years old, Is very famous here. (b) 介詞后不能用。 We depend on the la

43、nd from which we get our food. We depend on the land that/which we get our food from. 只能用that作為定語從句的關系代詞的情況 (a)在there be 句型中，只用that，不用which。 (b)在不定代詞，如：anything, nothing, the one, all等作先行詞時，只用that，不用which。 (c)先行詞有the only, the very,the same,the last,just修飾時，只用that。 (d)先行詞為序數詞、數詞、形容詞最高級時，只用that,不能用wh

44、ich。. (e)先行詞既有人，又有物時。 (f) 先行詞指物，在主句中作表語時 (g) 為了避免重復 (h)先行詞是the way或the reason時，that可作關系副詞，也可省略 (i) 主句的主語是疑問詞who /which時 舉例： Is this the book that you borrowed in the library? 這是你在圖書館借的那本書嗎？ Who that break the window should be punished 誰打碎了窗戶都要受到懲罰 All that is needed is a supply of oil. 所需的只是供油問題。 Fi

45、nally, the thief handed everything that he had stolen to the police. 那賊最終把偷的全部東西交給了警察。 that必用 1.先行詞是最高級或被最高級修飾 2.是序數詞或被序數詞修飾 3.不定代詞 4.先行詞即指人又指物 5.被only；the every，no，one of等修飾 6.主句有which；who；whom 7.there be 句型中 8.如果有兩個從句，其中一個關系代詞已用了which,另一個關系代詞宜用that 9.先行詞在主句中作表語，或者關系代詞本身作從句的表語是宜用that ,that在作賓語時可省 難

46、點分析 （一）限制性定語從句只能用that的幾種情況 1、當先行詞是anything, everything, nothing (something 除外), few, all, none, little, some等代詞時，或者是由every, any, all, some, no, little, few, much，each等修飾時 (1) Have you taken down everything (that) Mr. Li has said? (2) There seems to be nothing (that) seems impossible for him in the w

47、orld. (3) All that can be done has been done. (4) There is little (that) I can do for you. 注意1：部分時候that可以省略，如部分例句將that用括號括住。 注意2：當先行詞指人時，偶爾也可以用who (4) Any man that/.who has a sense of duty wont do such a thing. 2、當先行詞被序數詞修飾 The first place that they visited in London was the Big Ben. 3、當先行詞被形容詞最高級修飾

48、時 This is the best film that I have seen. 4、當形容詞被the very, the only，the same,the last ,any,little等修飾時 (1) This is the very good dictionary that I want to buy, (2) After the fire in his house, the old car is the only thing that he owned. 當先行詞指人時，偶爾也可以用who (3) Wang Hua is the only person in our school

49、 who will attend the meeting？ 5、當先行詞前面有who, which等疑問代詞時 (1) Who is the man that is standing there? (2) Which is the T-shirt that fits me most? 6、當先行詞既有人，也有動物或者物體時 Can you remember the scientist and his theory that we have learned? 7.當關系代詞在定語從句中做表語 The village is no longer the one that it used to be

50、10 years ago. 8.當在there be句型中，通常情況下用that，不用which （二）關系代詞as和which引導的定語從句as和which引導非限制性定語從句，有相同之處也有不同之處。具體情況是： 1、As和which都可以在定語從句中做主語或者賓語，代表前面整個句子。 (1) He married her, as/which was natural. (2) He was honest, as/which we can see. 2、as 引導非限制性定語從句，可放在主句之前，或者主句之后，甚至可以切割一個主句；which引導的非限制性定語從句只能放在主句之后。另外，as

51、有“正如，正像”的意思 (1) As is known to all, China is a developing country. (2) He is from the south, as we can see from his accent. (3) John, as you know, is a famous writer. (4) He has been to Paris more than several times, which I dont believe. 注意：當主句和從句存在邏輯上的因果關系時，常用which。 Tom was always late for school, which made his teacher angry. 3、當先行詞受such, the same修飾時，常用as (1) I have never heard such a story as he tells. (2) He is not such a fool as he looks. (3) This is the same book as I lost last week. 注意：當先行詞