逗号Comma

1.逗号用来分隔一系列单词、词组和句子，使用情况如下：

连接两个词或词组 A and B
连接两个句子 A, and B
连接三个及以上词，词组或句子 A, B, and C

※and 改为其他的连词（如：for，and，nor，but，or，yet，so）时，上述标点符号依然适用。

a. The pioneers labored to clear away the forest and to plant crops.（ A and B）
b. The little boy is only three years old, but he can take care of himself in the trip.（ A, and B）
c. Her dress is elegant, her speech is powerful, and everything she does attracts me.（ A, B, and C）

误： Secluded little islands in the Pacific are restful and, alluring.
正： Secluded little islands in the Pacific are restful and alluring.
解析：由于句子中restful和alluring两个形容词并列，用and连接，不应在and后面加逗号。SAT真题中，连词后面会出现多余的标点，这是常见的一种错误。

误： We met each other two years ago in a meeting but, you may not remember me.
正： We met each other two years ago in a meeting, but you may not remember me.
解析：we met each other和you may not remember me是两个独立的句子，中间用连词but来连接，在but前面添加逗号。

2.逗号用来分隔同位语或简短的插入语，但是不能分开主语本身，也不能在主语和谓语之间随意加逗号。

误： Chemical fertilization, for example helps to produce better crops, but is, harmful to the environment. 正： Chemical fertilization, for example, helps to produce better crops, but is harmful to the environment.
解析： for example做插入语，是说明这一句和上一句的关系的。插入语的前后用逗号与句子隔开。

误： Glory Foods' president, and founder Bill Williams, explains the unusual slogan by admitting that while he knows that his foods can' t beat the taste of real home cooking, they do come very close.
正： Glory Foods' president and founder Bill Williams explains the unusual slogan by admitting that while he knows that his foods can' t beat the taste of real home cooking, they do come very close.
解析：句中president和founder都是主语的一部分，不能用逗号隔开。另外，错误句中Bill Williams后面的逗号处于主语和谓语之间，这是不可以的，应去掉这个逗号

误： The retiring worker, was applauded more than she expected.
正： The retiring worker was applauded more than she expected.
解析： worker后面的逗号处于主语和谓语之间，不能在此处使用。

误： Once we' ve found artwork for the covers, editorial production, begins.
正： Once we' ve found artwork for the covers, editorial production begins.
解析：错误句中production 后面的逗号处于主语和谓语之间，不能在此处使用。

3.用逗号来分隔非限定性修饰语，即该修饰语对于句子的意义并非必不可少。

A brief comparison with the most famous chivalric drama, which was written fifteen years earlier, clarifies the uniqueness of Thon' s play.
句中which引导的定语从句不是句子不可或缺的一部分，如果把which从句去掉，剩下的部分仍是一个完整句子：
A brief comparison with the most famous chivalric drama clarifies the uniqueness of Thon' s play.
（把索恩的戏剧和最有名的骑士剧稍加对比，就可以发现索恩作品的独到之处。）

误： These satellites provide data, on land, ocean, and atmosphere conditions, that are crucial for many specialized uses.
正： These satellites provide data on land, ocean and atmosphere conditions that are crucial for many specialized uses.
解析：错误句子中第一个逗号没有必要，on land是介词短语修饰名词data，直接跟在data后面即可。另外，that前面的逗号也没有必要，因为that引导的定语从句都是限定性的，前面不能加逗号。