在英文中，使用逗号来隔开句子是用来标明语句中的停顿、分割不同部分、插入附加信息或提供结构上的清晰度。以下是一些使用逗号的常见情况：
1. 列举：逗号用于列举一系列项目、人或事物。例如："I like apples, oranges, and bananas."（我喜欢苹果、橙子和香蕉。）
2. 分隔主句和从句：逗号用于分隔主句和它所引导的从句。例如："I went to the store, but they were closed."（我去了商店，但他们关门了。）
3. 同位语：逗号用于标明同位语，即补充或解释前面名词的附加信息。例如："John, my best friend, is coming over tonight."（我的好朋友约翰今晚要来。）
4. 插入语：逗号用于标明句子中的插入语，即附加信息或注释。例如："The weather, as you know, is very unpredictable."（天气，正如你所知，非常不可预测。）
5. 数字分隔：逗号用于分隔大数字的千位数。例如："1,000"（一千）。
需要注意的是，逗号的使用也可因句子结构、上下文和风格等因素而有所变化。正确使用逗号的规则需要视情况而定，有时可能需要依赖语法规则、标点符号规范和个人写作风格的选择。
1. 在并列连词(and, but, for, nor, or, yet )前使用，用来连接句中的各分句。
The principal reason for this is that none of them possesses chlorophyll, andsince they cannot synthesize their own carbohydrates, they obtain their supplies either from the breakdown of dead organic matter or from other living organisms.
2. 用逗号来分隔一系列单词、词组和从句。
Furthermore the walls of fungal cells are not made of cellulose, as those of plants are, but of another complex sugarlike polymer called chitin, the material from which the hard outer skeletons of shrimps, spiders, and insects are made.
They are a major cause of structural damage to building timbers, a cause of disease in animals and humans, and one of the greatest causes of agricultural losses.
3. 逗号用来分隔与句子其他部分密切相连的简短插入语或旁白。(较长的，更为突兀的或复杂的插入成分的则用破折号或圆括号。)
Chemical fertilization,for example, helps to produce better crops, but is harmful to the environment.
4. 在并列形容词，即分别修饰同一个名词的形容词之间使用逗号，但也有的形容词之间不加逗号的。
For men, heroism was usually described as bravery and the active, successfulovercoming of adversity.
5. 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。非限定性修饰语与限定性修饰语的区别在于，它即使被省略，也不会改变句子的主要意思。
(1) 同位语
The canopy, the upper level of the trees in the rain forest, holds a plethora of climbing mammals of moderately large size, which may include monkeys, cats, civets, and porcupines.
(2) 从句
The canopy, the upper level of the trees in the rain forest, holds a plethora of climbing mammals of moderately large size, which may include monkeys, cats, civets, and porcupines.
7. 在以"月、日、年"为次序排列的日期间使用逗号。如果这种次序的日期出现在句子中间，则在"年"后也加上逗号。
Martin Luther King, Jr., was born on January 15, 1929, and died on April 4, 1968.
但在以"日、月、年"为次序排列的日期间，不使用逗号。
Martin Luther King, Jr., was born on 15 January 1929, and died on 4 April 1968
