Question

这句英语的语法结构

1：Paradoxically, relationships that seem perfect and in which the couple does everything together are at great risk of failing.

"in which" 在句里代表什么？怎样解释?
整句话应该如何的翻译？为什么加上了in which

Answer 1

in which引导一个定语从句，修饰relationship， 如果把其变为陈述句语序就是in the relationships, the couple does everything together，也就是说，in which后面的句子“the couple does everything together”是用于限定先行词“relationship”的定语。which为关系代词。
翻译：与之矛盾的是，看上去完美的，夫妇共同做每一件事的婚姻关系常常面临巨大的失败危险。
in which说明这段婚姻关系中，夫妇俩一起做每一件事，in 是与relationship相搭配的介词。

Answer 2

是定语从句的引导词，in which =where,where是疑问副词，相当于一个介词短语。一个介词+which有很多种意思，如：for which=why, at which=when, of which=whose, from which可以做方状,还有by which我不知道怎么解释的等等。但是介词+what不可以，what不能做定从引导词。

Answer 3

很矛盾的是，看起来很好的、并且夫妻一起做任何事情的这样一种交往关系面临着很大的失败风险。
in which 和之前的 that 是给 relationships 作并列后置定语引导从句的
主句：Relaitionships are at a great risk of failing.