19.3 原因狀語從句
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比較:because, since, as和for

1) because語勢(shì)最強(qiáng),用來說明人所不知的原因,回答why提出的問題。當(dāng)原因是顯而易見的或已為人們所知,就用as或 since。
  I didn't go, because I was afraid.
  Since /As the weather is so bad, we have to delay our journey.

2) 由because引導(dǎo)的從句如果放在句末,且前面有逗 號(hào),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。
  He is absent today, because / for he is ill.
  He must be ill, for he is absent today.















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