This is the house where he was born
=This is the house in which he was born （in 提到前面去了,后面就别在出现了）
=This is the house which he was born in （不说 in which 而是把 in 放在后面,也是对的）
第一句中的 where = in which.这个 where 不同于我们平时常用的 where is he?中的疑问副词 where,这里的 where,它等同于 in which,语法上叫做缩合连接副词.如果你有薄冰的《英语语法》,参看390页.