1. 两个个或两个以上的词、短语或句子只用一个并列连接词来连接，他们之间就要用逗号，规范语法要求并列连接词前也要用逗号英语中逗号comma的用法看似不重要，实则必须掌握，否则就是不规范。
There are three people in my family, and they are my father, my mother, and me.
He opened the book, read it and made a note of the contents.
2. 句子中的插入语，补充说明的部分，或同位语前后必须用逗号分开I own more than a thousand books and, to make matters worse, the room is rather limited.
After we had visited our friends, we returned home. = We returned home after we had visited our friends.
4. 非限制性定语从句必须用逗号五主句分开Thanks to the English Channel, which separates Britain from the mainland of Europe, the country has not been invaded since 1066.
Few drivers, however, completed the race due to the bad weather.
She feared the exam. She couldn’t, therefore, continue her study at school.
= She feared the exam. Therefore, she couldn’t continue her study at school.
As a result, they got to the place where were told to gather.
With some children, small money goes a long way.
Astonished by the heavy rain last night, the girl failed to fall asleep all through the night.
