是用來說明引起主句這個結果的原因的從句，在初中階段引導原因狀語從句的從屬連詞主要的有because, as, since,for等。例如：

1.I didnt go to school yesterday because I was ill. 　　我昨天沒去上學，因為我生病了。

2. Since everybody is h ere, lets begin our meeting. 　　既然大家都來了, 讓我們開始開會吧.

3. As you are in poor health, you should not stay up late. 　　既然你身體不好, 你就不該熬夜.

4.I asked her to stay to tea, for I had something to tell her. 我請她留下來喝茶,因為我有事要告訴她.

原因狀語從句應注意的問題

1、because , since , as , for,辨析

1)because語勢最強，用來說明人所不知的原因，回答why提出的問題。當原因是顯而易見的或已為人們所知，就用as或 since。

I did nt go, because I was afraid.

Since /As the weather is so bad, we have to delay our journey.

2)由because引導的從句如果放在句末，且前面有逗 號，則可以用for來代替。但如果不是說明直接原因，而是多種情況加以推斷，就只能用for。例：

He is absent today, becaus e / for he is ill. 　　He must be ill, for he is absent today.

3) as和for的區別：通常情況下，as引導的從句在主句前，for引導的從句在主句后。例： 　　As the weather is cold, I stay at home.(同義句) 　　I stay at home, for the weather is cold.

2、because習慣上不與so連用

漢語習慣上說因為所以，但英語習慣上卻不能將 so與because 連用：

正：Because it was raining, we stayed at home. / It was raining, so we stayed at home.

誤：Because it was raining, so we stayed at h ome. 因為下雨，所以我們呆在家里。

3、because 從句與 because of短語的轉換

Because引導的原因狀語從句有時可與because of 短語轉換，because of后加的原因可以為好或壞 ，但最正規的還是because。

He cant come because he is ill. / He cant come because of his illness. 他因病不能來。

I said nothing about it because his wife was there. / I said nothing about it because of his wifes being th ere. 因為他妻子在那兒，我對此事只字未提。

常見考法

對于原因狀語從句的考查，多以單選和完形填空的形式，從連詞的意義角度讓大家選擇連詞。

典型例題：He fou nd it increasin gly difficult to read, ____ hi s eyesight was beginning to fail.

A. and B. for C. but D. or

解析： his eyesight was beginning to fail是he found it increasingly difficult to read的原因， 因此本題應選用可以表示原因的連詞for引導原因狀語從句。

答案： B

誤區提醒

除了because , since , as , for這四個詞的辨析外，對于because 從句與 because of短語的區分也是難點之一。Because引導的原因狀語從句有時可與because of 短語轉換，because of后跟的是短 語 ，because后跟的是句子。

典型例題：He didnt go to work the heav y rain.

A .because B.because of C.so D.since

解析：題干的意思是 由于那場大雨，他沒有去上班 ，the heavy rain.表示原因，排除C; since 和 because 表示原因，后面跟的是從句，也就是說必須是一個完整的句子，本題中the heavy rain沒有主語和謂語，.只是一個短語，所以排除A和C;because of表示由于，后跟名詞、代詞或短語。

答案：B

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