回複：搞學問前先端正態度，要不免談，你說呢？

I don’t know exactly what happened between you two.  I am only commenting on “which”.  J

Let’s use his sentence for example, “You did make a lot of efforts and chose words carefully to express your ideas, which are good.”    It is common in spoken English where "which" is loosely used, but it should be avoided in written English.  The reason is that “which” is used as a pronoun here.  But what exactly does it refer to?  If “which” refers to the whole process of making efforts to express ideas, then it should be “which IS good”, not "are", passable in spoken English.  If “which” refers to “ideas”, then delete comma and use “that”.  That is why he is correct on pairing which with a comma, but not quite confusing. Either way, the sentence has a grammatical error. 

"You did make a lot of efforts and chose words carefully to express your ideas, which are good" ==> has grammatical error.
You did make a lot of efforts and chose words carefully to express your ideas, which is good ==> common and passable in spoken English
You did make a lot of efforts and chose words carefully to express your ideas that are good ==> grammatically good, but confusing in meaning