english problem

This may have something to do with the TV commerical in which the characters are usually portrayed as a sex symbol.

我想問下in which 點解??岩岩睇到話in which =where ,咁tv commerical 好似唔關地方時咁點解要用in which , 答: in which = in the TV commercial 在電視廣告裡的...(人物)
用which 得唔得??
答: 不得, 因為少了 in 就沒有了"在...(.電視廣告.)..裡的(人物)...." 的意思, 單表示電視廣告
e.g. in the car = in which; 在車裡, 沒有了 in , 單指車
問: it would be wiser for us to be more rational
我想問下wiser for 點解啊??
答: 句子分為三部份: It is wise/ for us / to be more rational.
wise 有智慧/ 聰明
for us 對我們 to be more rational 要是更理智 sentence structure 句式= It is + adj + for (人) + to infinitive = we are wise to be more rational 全句= 我們要是更理智是(顯示)我們有智慧。
e.g. It is wise for her to leave him. 她離開他(顯示)她是聰明的。

It would be wiser for us to be more rational
你分拆錯了，不應將 wiser for 合併。
應該是：it would be wiser / for us to be more rational.
“to be more rational” 是指這樣做才是 wiser 的行徑 ，而人物是“for us”.

這句的意思是： If we are rational, we are wise.

Since in which=where=where the characters are=relative pronoun to stand for "TV commercial".
Since wiser for cannot be separated,it should be for us=for=preposition=a preposition help to express purpose.eg:-On rewritten:-
It would be wiser to be more rational for us.