请大神分析下这句子里的语法点,
问题描述：
请大神分析下这句子里的语法点,
Urgently,he teaches her about Descartes,who doubted,and by doing so knew at least that he could doubt.
答
被修饰的词叫先行词.定语从句不同于单词作定语的情况,它需要放在被修饰的词（即先行词）之后.定语从句一般由关系代词来引导.关系代词必须放在定语从句之首.定语从句（Attributive Clauses）在句中做定语,修饰一个名...