for
单词辨析：
语气最强，表示因果关系，通常用来回答由 why 引导的疑问句。由 because 引导的分句置于句首时，须用逗号与主句隔开，置于句末时则不用隔开。
Because the traffic is so busy, she failed to arrive at the station on time.
因为路上交通太拥挤，她没能准时赶到车站。
He came back late because there was something wrong with his car.
他回来晚了，因为汽车出了故障。
如果所述理由是明显的或者已知的，则用 as 较 because 更为合适。
As it's raining, you'd better stay at home.
既然在下雨，你最好呆在家里。
He puts the ice cream into the fridge immediately, as it melts easily.
他马上把冰激凌放进冰箱，因为它很容易化掉。
for 属于并列连词，由它引导的分句表示补充说明性的理由，通常只能置于句末，且必须用逗号与前面的分句隔开。
He must have passed this way, for here are his footprints.
他肯定是从这条路走过去的，这里有他的脚印。
He has to work hard, for he wants to support his family.
因为要养家糊口，他必须努力工作。
当所述原因是已知的客观事实或被当作推断的理由时用 since，语气略强于 as。
Since he is absent, let's begin.
既然他不在，我们就开始吧。
Susan must have come back home, since her coat is not in the wardrobe.
苏珊肯定回过家，因为她挂在衣橱里的外套不见了。
相关例句：
He had a great desire to have a home of his own for he had always lived with my grandmother.
他强烈渴望拥有一个属于自己的家，因为他一直和我祖母住在一起。
Another union has voted for industrial action in support of a pay claim
另一个工会已经投票赞成采取要求加薪的劳工行动。
It might be possible for a single woman to be accepted as a foster parent
有可能会接受单身女子作为领养人。
The Brady Bill is named for former White House Press Secretary James Brady
布雷迪法案是以前白宫新闻秘书詹姆斯·布雷迪的名字命名的。
I knew he worked for a security firm
我知道他在一家保安公司工作。
If your pharmacy doesn't stock the product you want, have them order it for you
如果药店没有你想要的药品，让他们为你订购。