we are living in an age which we have a lot of things to lea

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关系代词which代替的先行词是age；换言之,关系分句 which we have a lot of things to learn about修饰的先行词是age.
which在从句中作介词about的宾语,就是说we have a lot of things to learn about the age.
which是关系代词,在从句中只能作主语、宾语或表语,是绝对不会作状语的,只有关系副词才可以作状语.完全可以把about提到which前,这样问题就更好理解了.
这句话的意思是：我们生活在一个【有许多东西还不为我们了解的】时代.
——【译苦思甜】团队成员回答