狀語從句（一）

 a.because
 because因為
 because i like it, i do it.
 因為我喜歡，所以我才干。
 he couldn'thave seen me, because i was not there.
 他不可能見過我，因為當時我不在那兒。

 比較：
 because 和for的區(qū)別。
 1.for 是并列連詞，只用于連接表示原因的分句，因此不能用于句首。because表示原因時，可位于句首。
 【誤】for he did not obey the rules, he was punished.
 【正】because he did not obey the rules, he was punished.
 由于他不遵守規(guī)章制度，他受到了處。
 2.for 表示的是推斷解釋，because強調(diào)動作發(fā)生的直接原因。
 it must have rained last night, for the ground is wet.
 昨晚肯定下雨了，因為地面是濕的。（不可用because，因為地面濕不是天下雨的原因）
 the day breaks, for the birds are singing.
 天亮了，因為鳥在叫。（不可用because，因為鳥叫不是天亮的原因）
 he went to bed early, because he was tired
 由于他累了，所以他很早就上了床。（直接的理由）
 he must be tired, for he went to bed early.
 他肯定累了，因為他很早就上了床。（間接的推斷）
 3.在強調(diào)結(jié)構(gòu)it iswas�that和關(guān)聯(lián)詞not�but 引導的原因狀語從句中，宜用because。
 it's because he helped you that i'm prepared to help him.
 正是因為他幫助過你，所以我樂意去幫助他。
 he decided to give up thechance of going abroad, not because he did not want
 to but because his wife was ill.
 他決定放棄出國的機會，不是因為他不想去，而是因為他妻子病了。

b. since

 since 因為，既然。引導的從句大多置于句首，主從句的時態(tài)一般相同。
 since you have no licence, you are not allowed to drive.
 因為你沒有駕駛執(zhí)照，所以不允許你開車。
 since you are al here, let's try and reach a decision.
 既然大家都來了，咱們就設法做出一個決定吧。

 c.as
 as 由于。一般多用于句首。
 as she was ill, she didn't come to the party.
 由于病了，她沒來參加晚會。
 as he was not well enough, i had to go without him.
 由于他身體欠佳，我只好不帶他去了。
 as it rained, we all stayed at home.
 由于下雨我們都呆在家里。

c. because, since, as 的區(qū)別

 1.because語氣最強，表達的是未知的新信息，一般置于主句之后，也可以放在主句之前，用逗號隔開。在回答why引導的特殊疑問句時，或在強調(diào)結(jié)構(gòu)it iswas �that 和關(guān)聯(lián)詞not �but 引導的原因狀語從句中，要用because。另外，because還常和副詞just, merely等連用。
 2.since 往往表示的是已知的客觀事實，或分析后的推理，引導的從句大多置于句首，主從句的時態(tài)一般相同。
 3.as 表示的理由最弱，只是對主句的附帶說明，重點在主句。as從句通常放在主句前。
 just because he doesn't complain, you must not suppose that he is satisfied.