because, as, since, for, 的区别 because的用法： 通常表示直接而明确的原因和理由，语气很强，用来回答why的问题, 多放于主句之后。 例：We couldn't go out because it was too cold. 因为天气太冷，我们不能外出。 as的用法： “因为、由于”，语气比because弱，表示的是不言而喻、显而易见的原因和理由，其从句一般放在主句前。 例: As it was late ,we came back soon. 由于时间很晚了，我们很快就回来. As rain has fallen, the air is cooler. 因为下过雨，空气比较清爽。 Since的用法: “既然”, 语气较弱，强调已知的事实，其从句一般放在主句前。 既然你回答不出这个问题，我就问别人了。 例：Since you can't answer the question, I'll ask someone else. 既然他的方法不行，我们就试试你的吧. Since his method doesn't work, let's try yours. 既然你对此如此有把握，他会相信你的。 Since you are so sure of it, he’ll believe you. For的用法：并列连词，表示对前一分句补充说明，放在句末。 例：It must be morning for the birds are singing. 一定是清晨了，因为鸟儿在叫。 It will rain, for it’s getting dark。 要下雨了，因为天气越来越暗了。 because since as for 因为 因为 既然 由于 意义 强调未知原因 位置 多后置 常前置 表示已知显然的理由 常前置 常用于推断、补充解释 后置 例如：He introduced me because I was new. Since you are going, I will go, too. As it is raining, you’d better take a taxi. It must have rained last night, for the ground is wet. 本文来源：https://www.wddqw.com/doc/d693f7af5901020207409cdb.html