求教：一条高一定语从句的问题

题目

求教：一条高一定语从句的问题
Is this pen_________you lost yesterday?
补充成定语从句的话 是不是填the one which
但如果直接what可不可以呢
Suzhou,where I spent my childhood,I have never been back to.
这句话有没有问题？要表达这个意思，应该怎么说？
The reason for which he was late for school is that he got up late this morning.
请问这个句子要怎么理解？这个which代什么呢？

答案

不可以填the one which,因为在定语从语句中先行词如果是不定代词如onesomething等,只能用that引导该定语从句.what不可以直接用在这里哦