英语的定语从句,哪些情况从句与主句之间要加逗号?

非限制性定语从句和主句之间有逗号.判断限制性还是非限制性要看从句和主句的关系.如果从句对主句来说不可或缺,少了主句意思不完整,就是限制性定语从句,如：Do you remember the place where we visited last week?而非限制性定语从句是对主句的一个补充说明,去掉主句意思依然完整,如,He came back yesterday,which made his parents very happy.再如,2008 Olympic Games was held in Beijing,as we all know.