we have received your enquiry of 15 october_in which_ you advise us of your interest in cashmere.

题目

we have received your enquiry of 15 october_in which_ you advise us of your interest in cashmere.
此句为什么要选in which?
we have received your letter of septembe 12,_____ we are glad to know that you are interested in our electric heaters.( which at which in which from which）要选哪个答案呢?

答案

in which 是一个非限制性定语从句的用法,具体是指in your enquiry,in which在此处做状语.你的这个句子有点像商业用语.
第二个句子我个人认为要选from which,具体是指from your letter,也是充当状语的成份.而且这个句子也有点像商业用语.
是吗?