到底主语中”は”和”が”在意思上的区别是什么

”お客さんが中国からきます””お客さんは中国からきます”どれは正しいですが。

王さん昨日午後に来ましたが。 this sentence the"に”,can it be cancelled?昨日午後王さんきましたが。

does "associate" has a meaning of "vice","associat degree" what is it ?

"be wasted on " what is the meaning of the expression ? "be wasted on " what is the meaning of the expression ?our textbook said it means "not understand sth or not realize how valuable sth is". but why i feel it is not proper when i take it into a sentence ,it feels strange.

now i have doubt about a word" idealistic" now i have doubt about a word" idealistic".what is the definition of this word?it means that someone who is too optimistic to think everything has access to achieve and opposed to "realitisc" or it means someone who has a dream and a goal and he never lose heart and try to get it !who can help me ?

what is the meaning of "remark"? i some what is the meaning of "remark"? how can it be used ? and a detailed example is needed!