as 和because表原因的时候用法有什么不一样的?

because引导原因状语从句语气最强，表示直接原因,常用来回答由why提出的问题，所引导从句可放在主句前，也可放在主句后。
例如：
"Why did you do it?""Because Carlos told me to".
We can't go to Julia's party because we'regoing away that weekend.
Because he didn't catch the last bus, hehad to walk home.
Why are you late for school ? Because I missed the first bus.
as “由于,鉴于” 主从并重，从句说明原因，主语说明结果。说明比较明显的原因。多用于日常语中，常译为“由于”，从句一般放于主句前。
例如：
You can go first as you're the oldest.
As you don't feel well, you had better stayat home.
As he wasn't ready in time, we went withouthim.
I must stop writing now, as I have rather alot of work to do.
As it was getting late, I decided to bookinto a hotel.
As it is raining, you'd better take a taxi.
拓展：since和for也能表示原因
since “因为,既然” 侧重主句，主句表示显然的或已知的理由。强调说话者和听者双方都知道的原因，常译为“既然”，一般用在这样的句子里。
例如：
Since we've got a few minutes to wait forthe train, let's have a cup of coff