没有倒装的必要，不是介词放在which前都要倒装的。
当关系代词在定语从句中作介词宾语时，我们通常用“介词＋关系代词”引导定语从句。如果指“人”，用“介词＋whom”如果指“物”，用“介词＋which”：
This is the house in which we lived last year. 这是我们去年居住的房子。这个句子相当于This is the house which we lived in last year.介词+关系代词引导定语从句时，介词往往受上下文的约束：
(1) 从先行词跟介词的搭配习惯出发。
如：In front of my house， there is a tree， in which some birds are singing. 我的房子前有一棵树，鸟儿正在树上唱歌。(在树上一般用介词in)
(2) 从定语从句中的动词、形容词对介词的习惯要求出发。
如：The computer for which I paid 5，000 yuan is made in Shenzhen. 我花了五千元所买的这台电脑使深圳造的。( pay 与for搭配)
(3) 从先行词、定语从句中的动词或形容词两方面同时考虑出发。
如：Do you know the girl with whom the man talked just now? 你认识跟那个男谈话的女孩吗
(4) 复合介词+关系代词。
如：Go down this road， at the end of which you can see a high building and it is our office building. 沿着条路走，在路的尽头你会看到一座高大的建筑，那就是我们的办公大楼。
(5) 名词/代词+介词+关系代词。如：I saw three camp beds， two of which were occupied. 我看见了3张折叠床，其中两张已有人占了。倒装的情况
比如 ：in the midst of which （the two hills）a great river flowed经过了倒装，变成了in the midst of which （the two hills）flowed a great river谓语flowed放到了主语a great river之前。这是因为in the midst of which （the two hills）是地点状语，地点状语放句首，句子可以倒装。同时in the midst of which是介词短语+which结构，从句可以倒装
