1）关于连词连接句子：
She knew she was near the shore because the light was high up on the cliffs.
The man wanted to fly to Rockall, a lonely island in the Atlantic Ocean, but Captain Fawcett did not take him because the trip was too dangerous.
以上两句because前没逗号
He was amused too, because he never expected the bicycle to be found.
这句because又加了逗号
那样because前加不加逗号的不同之处呢？
2）关于时间状语
One afternoon she set out from the coast in a small boat and was caught in a storm.
During that time she covered a distance of eight miles.
以上两句前的时间状语后没逗号
Towards evening, the boat struck a rock and the girl jumped into the sea.
Early next morning, she saw a light ahead.
同样是时间状语，这两个句子后又加了逗号，这是为何呢？
1）关于连词连接句子：
She knew she was near the shore because the light was high up on the cliffs.
The man wanted to fly to Rockall, a lonely island in the Atlantic Ocean, but Captain Fawcett did not take him because the trip was too dangerous.
以上两句because前没逗号
He was amused too, because he never expected the bicycle to be found.
这句because又加了逗号
那样because前加不加逗号的不同之处呢？
because引导是什么原因状语从句的正常地方是主句之前。假如主句不是非常长，主句和because从句之间不需要逗号，但主句末会用降调，从句末再用降调。即主句和从句为二个语调群。二个语调群之间可以用逗号，也可以不需要逗号，主要靠语调加以区别。
第三句之所以用了逗号，是由于副词too的用法，too作为联加状语，一般用逗号和句子其它部分隔开。假如去掉too，则because前的逗号可以不需要。
假如because从句置于主句之前，则为强调缘由状语，此时从句与主句之间需要用逗号。
假如主句为否定句，because从句在主句之后，此时假如用逗号，表示缘由从句不在not的否定范围之内。假如不需要逗号，则一般not的否定范围延伸到句末。比如：
I didnt do it, because I loved you. 由于我爱你，所以我没做那件事。（否定范围不包含从句）（二个语调群，主句读降调，从句再读降调。）
I didnt do it because I loved you. 我不是由于爱你才做那件事的。（否定范围延伸至句末）
（一个语调群。主句和从句之间用平调过渡。）
2）关于时间状语
One afternoon she set out from the coast in a small boat and was caught in a storm.
During that time she covered a distance of eight miles.
以上两句前的时间状语后没逗号
Towards evening, the boat struck a rock and the girl jumped into the sea.
Early next morning, she saw a light ahead.
介词短语作状语坐落于句首，假如介词短语不长，一般无需用逗号，但该状语要读升调。
假如介词短语较长，则一般用逗号和主句隔开，仍然读升调。
书面语中的逗号，对应于口语中的停顿。停顿发生在乎群和意群之间。停顿可以用于说话时的换气，停顿也可以表示强调，引起听话人的期待。意群之间是不是停顿，取决于前一个意群是不是非常长，与后一个意群是不是需要强调。
