in which = in books 在书中
which 是引导定语从句in which heroes fight against their enemies的关系代词,代替先行词books
请在客户端右上角评价点“满意”即可,所以这个句子也可以写成My father likes reading books which heroes fight against their enemies in吗？OK!!!!!!in 也可以置于关系代词which 之前， 即： in whichin which 又等于where