虽说逗号是我们非常常用的标点符号，几乎每个句子都出现，但是在写作中，也会经常出现一些我们没有意识到的错误。
01
插入补充部分
in parenthetical statements
插入部分可以理解为是一个完整句子的补充部分，即可以用括号围起来的部分。少了这部分内容句子也是完整的。当用逗号分隔插入部分语句时，它的作用跟括号是相似的：
1. 当出现在句子中间时，逗号永远是成对出现的。
The inhibitor genistein, known to be selective for tyrosine kinases, unexpectedly inhibited this serine kinase-mediated response also.
2. 如果插入部分位于句子尾端，可以只出现一个逗号。
The reaction was inhibited by C3 toxin, a selective blocker of Rho.
3. 单独一个词（或简单的短句）作为插入部分，不需要用逗号。
þ The protein kinase inhibitor genistein did not alter the response.
ý The protein kinase inhibitor, genistein, did not alter the response.
4. and和but要引导插入部分要用逗号跟主句分开。
þ The control cells showed modest internalization but,contrary to our hypothesis, drug-treated cells showed even less internalization.
ý The control cells showed modest internalization, but contrary to our hypothesis, drug-treated cells showed even less internalization.
同一个道理，这个句子去掉插入部分也必须是一个完整的句子！
02
在复合句中
in compound sentences
1. 在复合句中，通常没有“..., and...”这种写法，除非“and”两边的句子是独立的，即两边的句子都有自己的主语和谓语。而如果一个句子中出现“and”，但是没有逗号，那么“and”连接的分句不需要有另外的主语。
ý The cells were pretreated with pertussis toxin for 24 hr, and lysed by scraping in a hypotonic buffer.
这个句子的主语是“cells”，但是逗号后面“and”引导的句子没有另外的主语，所以这个句号应该要把逗号去掉。
þ The cells were pretreated with pertussis toxin for 24 hr and lysed by scraping in a hypotonic buffer.
2. 不能滥用逗号来分隔长句。
对于长句，最好的处理办法是用句号或者分号将其分为两句。
ý For long sentences, the better alternative is to make them two separate sentences, with either a period or a semi-colon separating them, rather than using lots of commas, which I find annoying, and others will also, so avoid doing this.
þ For long sentences, the better alternative is to make them two separate sentences. Use either a period or a semi-colon separating them, rather than using lots of commas. I find excess commas annoying, and others will also. Annoying your readers should always be avoided!
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