如题所述
因为是直接原因的表达方式，表示听话人可能不知晓的因素，语气最强烈，通常用以回答why的提问。
例句：I stayed at home because it rained. 因为下雨，我待在家里。
I do it because I like it. 我这么做是因为我喜欢。
而since则侧重于主句，从句描述的是已为人所知的理由，语气较因为稍弱，常置于句首。
例句：Since he asks you, you'll tell him why. 既然他问你，你告诉他原因吧。
Since many of the customers work during the day, Billy has to collect the money at night. 许多顾客白天上班，所以毕利必须在夜晚去收款。
as用语则较为温和，常表示已知的事实或显而易见的原因，语气比since更弱。它更多地强调主从句的并重关系。
例句：We all like her as she is kind. 我们都喜欢她，因为她善良。
As I had a cold, I was absent from school. 因为我感冒了，所以没去上课。
例句：I stayed at home because it rained. 因为下雨，我待在家里。
I do it because I like it. 我这么做是因为我喜欢。
而since则侧重于主句，从句描述的是已为人所知的理由，语气较因为稍弱，常置于句首。
例句：Since he asks you, you'll tell him why. 既然他问你，你告诉他原因吧。
Since many of the customers work during the day, Billy has to collect the money at night. 许多顾客白天上班，所以毕利必须在夜晚去收款。
as用语则较为温和，常表示已知的事实或显而易见的原因，语气比since更弱。它更多地强调主从句的并重关系。
例句：We all like her as she is kind. 我们都喜欢她，因为她善良。
As I had a cold, I was absent from school. 因为我感冒了，所以没去上课。
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