请问什么时候用非限制性定语从句,为什么用限制性定语从句就可以吧句子的意思表达出来但还要用呢?
比如这题：1 My best friend is a great sports fan,I see her every day.
答案是：My best friend,I see every day, is a great sports fan.
为什么不可以直接：My best friend who I see every day is a great sports fan.
2 I often go to school with zhenhui,she lives in the same building as me .
答案： I often go to school with zhenhui,who lives in the same building as me .
为什么不可以直接：I often go to school with zhenhui who lives in the same building as me .
为什么不用加逗号句子就可以成立,而偏偏还有一个非限制性定语从句,要加逗号.在平时怎么判断什么时候要用非限制性,什么时候用限制性呢?两种用法除了逗号以外还有什么区别呢?
先谢过大家了!恕本人理解力较差,请解析得详细一点喔!