1、罗列事物或短语时用逗号隔断。
例:
I bought bread, cheese, and pickles at the grocery store.
我在杂货店买了面包、奶酪和泡菜。
2、需要分隔两个独立的较长从句,并使用连接词连接时:
例:
Astronomers have known about the positions of stars for centuries, but they didn’t understand that the earth revolves around the sun.
天文学家几个世纪以来就知道恒星的位置,但他们不知道地球绕着太阳转。
3、在介绍性短句的后面:
例:
In preparation for the next convention, the representatives studied up on the most important issues.
在为下一次会议作准备时,代表们研究了最重要的问题。
4、当需要区分附加说明部分的句子(parenthetical phrase),或要分隔插入语(interrupter)时:
例:
All doctors, if they care about their patients, are concerned with good office hygiene.
所有关心他们的病人的医生都关心良好的办公室卫生。