若是修饰句子的定语从句,which后加逗号吗？

先纠正一下你的问题。你的问题应当是修饰主句的定语从句，which前加逗号，而不是‘修饰句子的定语从句，which后加逗号’。
逗号应当加在‘which’的前面，而不是加在‘which’的后面。例句如下仅供学习定语从句参考，不推敲其他时态等。
1. My company sets up a new rule for us, which causes the employees unsatisfied.
2. A new regulation was just put into effection, which built up a new atmosphia in this region.

可以的啊 如a clean environment can help the city bid for the Oplympics, which ，in turn ，will promote its economic development

莫有莫有，后面有的话那叫啥句(⊙o⊙)？，四不像句

不加