we are not conscious of the extent ______work provides the psychological

we are not conscious of the extent _______work provides the psychological satisfaction that can make the difference between a full and an empty life
"______"处为什么用to which

extent是程度;限度;范围的意思
经常与to连用，例如：To a certain extent，从某种程度上说
在这里，也是同样的道理，而which则是与后面的句子相连，作为疑问词来补充成分，which work provides the psychological satisfaction that can make the difference between a full and an empty life.这实际上是一个完整的句子。

全句的意思是：我们并不太清楚要区分一个有意义的和空虚的人生需要多大程度的精神满足。

we are not conscious of the extent （我们不关心xxx程度）（后面整句是定语从句修饰前面的程度）to which work provides the psychological satisfication （工作提供的满足感）that can make the difference between a full and an empty life（定语从句用来修饰前面的满足感） 整句翻译：我们没有意识到工作提供的心理满足，可以充实的生活与空虚的生活之间的差异