因为句是主语从句,what 既可以引导主语从句,并且又可以在从句中作成分,what在本句的主语从句中作主语.而which, as, that 引导的是定语从句,并且前面必须有先行词,而what前面不用先行词,即 先行词+ that / which = wh...什么是“先行词”老师能举个例子吗？先行词是定语从句中被修饰的名词，如 This is a book that he gave me. 这是他送给我的书。这句中的book就是先行词。 你上面的句子，其实也可以加上一个先行词，然后用that或which 引导，变成定语从句，即 In some countries the schools that are called 'public schools' are not owned by the public.