as 从属连词，语意较because,since弱，着重在主句，所表示的原因或理由是“附带的”。
because 从属连词，语意强，着重直接的原因或理由，所引出的从句是全句的重心，用以回答why提出的问题。
for 并列连词，语气较弱，所引出的句子一般放在后面，表示附带说明的理由或推断理由。
since 语意比because弱，但比as强，一般用于表示“由于大家已知的事实”。
参考例句
1. The board split as I sawed it. 这块木板锯着锯着就裂开了。
2. Women can do as well as men. 女人可以做得和男人一样好。
3. Success in teaching, as in most areas of life, depends almost entirely on your attitude and your approach. 同人生中的大多数领域一样，教学上的成功几乎完全依赖你的态度和方法。
英英解释
n.
1. a very poisonous metallic element that has three allotropic forms; arsenic and arsenic compounds are
2. a United States territory on the eastern part of the island of Samoa adv.
1. to the same degree (often followed by `as')
