讲一下since当既然的时候怎么用?（主要是时态）

Question

讲一下since当既然的时候怎么用?（主要是时态）

Answer 1

1. since表示“既然”引导原因状语从句,且该从句一般放在主句之前,和now that用法一样.
至于其时态,没有绝对的限制或规定,关键是看主句和从句的动作发生的时间及语意.
如：Since you are free, why not go shopping with me?
Since you were late again, you should be punished.
Since you have finished your work, I'll phone you tomorrow.
2. since的用法已经在上面说明,不在复述了；
1）because表明直接的因果关系,语气最为强烈,可以回答以why提问的问句,且其引导的从句的位置不限；
如：--Why were you late this morning? --Because I got up late.
2）as一般表示众所周知的原因,语气较弱.且其引导的从句一般只放在主句之前.
As he is a boy, he knows a little about Chinese history.
3）for是一个并列连词,等同于and,后加分句表示对前面的内容进行补充说明而已.注意：for引导的从句必须要放在主句之后；该原因不一定就是正确的原因,只是说话人一种臆测而已.
如：He must be at home, for the light in his room is on.
但是：“房间灯是亮的”,并不一定就表明“他就在家里”.