as和 which都可指代前面一句話，請看例句:

1)Alice received an invitation from her boss, which came as a surprise.

愛麗絲受到了她老板的邀請，這使她感到吃驚。

2)The weather turned out to be very good, which was more than we could expect.

天氣結果變好了，這是我們沒有預料到的。

若有否定as錯;

3)The result of the experiment was very good, _______ we hadn't expected.

A. when B. that C. which D. what

【簡析】答案是C。由于非限定性定語從句是否定結構，只能用which引導，不能用as來替代which。

句首只能用as,還有認知猜想詞;

置于句首時，非限定性定語從句只能用as引導。例如：

As is known to everybody, the moon travels round the earth once every month.

眾所周知，月亮每月繞地球一周。

與表示認知猜想的詞，如know, expect, see, report, 連用時，要用as。

1)As we know, smoking is harmful to one's health.

我們知道，吸煙對健康有害。

2)As is expected, his daughter entered a key university.

正如人們所期望的那樣，他的女兒考入了一所重點大學。

固定結構用as, the same /such/so/as;

1) 在the same …as….結構中。意思是 “像……一樣的”。 例如：

Chongqing is not the same city as we have seen in other places.

重慶和我們在其它地方看過的城市不一樣。

注意區(qū)分: the same ….that….,請看例句：

This is the same pen that I lost. 這正是我所丟的鋼筆。(同一)

This is the same pen as I lost. 這支鋼筆和我丟的那支一樣。(相似，不是一個)

2)在as...as結構中，意思是“像……那樣的”。例如：

No period in history has had as many important changes _______ have taken place in the past century. 沒有哪個歷史階段像過去的一個世紀這樣有如此多的重大變化。

3)在such…as…結構中, 意思是“像……那樣的”。例如：

Mathilde had to work hard day and night and bought such a diamond necklace as she had lost to pay back to Jeanne.

馬帝爾德不得不日日夜夜地干活，來買一個像被她丟掉的那樣的鉆石項鏈還給讓。

So /such …that賓不離，so/such…as賓要棄;

在so/such…that結構中，that后引導的不是定語從句，而是狀語從句，從句中必須有賓語;在so/such…as結構中， as后引導的是定語從句，從句中不帶賓語。

例如：

1)He studies in such a good school that all other students in his village admire him.

他在那樣好的一所學校學習，以至于村子里其他的學生都很羨慕他。

解析：that后是狀語從句，狀語從句中有賓語him。

2)He studies in such a good school as all other students in his village admire.

他在那樣好的一所學校學習，村里的其它學生都很羨慕那所學校。

解析：as后是定語從句,as代替先行詞school,在定語從句中做admire的賓語。

as和 which都可指代前面一句話，請看例句:

1)Alice received an invitation from her boss, which came as a surprise.

愛麗絲受到了她老板的邀請，這使她感到吃驚。

2)The weather turned out to be very good, which was more than we could expect.

天氣結果變好了，這是我們沒有預料到的。

若有否定as錯;

3)The result of the experiment was very good, _______ we hadn't expected.

A. when B. that C. which D. what

【簡析】答案是C。由于非限定性定語從句是否定結構，只能用which引導，不能用as來替代which。

句首只能用as,還有認知猜想詞;

置于句首時，非限定性定語從句只能用as引導。例如：

As is known to everybody, the moon travels round the earth once every month.

眾所周知，月亮每月繞地球一周。

與表示認知猜想的詞，如know, expect, see, report, 連用時，要用as。

1)As we know, smoking is harmful to one's health.

我們知道，吸煙對健康有害。

2)As is expected, his daughter entered a key university.

正如人們所期望的那樣，他的女兒考入了一所重點大學。

固定結構用as, the same /such/so/as;

1) 在the same …as….結構中。意思是 “像……一樣的”。 例如：

Chongqing is not the same city as we have seen in other places.

重慶和我們在其它地方看過的城市不一樣。

注意區(qū)分: the same ….that….,請看例句：

This is the same pen that I lost. 這正是我所丟的鋼筆。(同一)

This is the same pen as I lost. 這支鋼筆和我丟的那支一樣。(相似，不是一個)

2)在as...as結構中，意思是“像……那樣的”。例如：

No period in history has had as many important changes _______ have taken place in the past century. 沒有哪個歷史階段像過去的一個世紀這樣有如此多的重大變化。

3)在such…as…結構中, 意思是“像……那樣的”。例如：

Mathilde had to work hard day and night and bought such a diamond necklace as she had lost to pay back to Jeanne.

馬帝爾德不得不日日夜夜地干活，來買一個像被她丟掉的那樣的鉆石項鏈還給讓。

So /such …that賓不離，so/such…as賓要棄;

在so/such…that結構中，that后引導的不是定語從句，而是狀語從句，從句中必須有賓語;在so/such…as結構中， as后引導的是定語從句，從句中不帶賓語。

例如：

1)He studies in such a good school that all other students in his village admire him.

他在那樣好的一所學校學習，以至于村子里其他的學生都很羨慕他。

解析：that后是狀語從句，狀語從句中有賓語him。

2)He studies in such a good school as all other students in his village admire.

他在那樣好的一所學校學習，村里的其它學生都很羨慕那所學校。

解析：as后是定語從句,as代替先行詞school,在定語從句中做admire的賓語。