如何判断定语从句的先行词是哪一个？？

Question

如何判断定语从句的先行词是哪一个？？我看到过两个例句，我说的是when与where
1.I was born in a town in the 1960s，when...
2.Every year sees the largest migration on the planet when...
为什么第一句不用where，第二句不用where?
PS：这些都是高考题

Answer 1

when 指代表示时间的先行词，where 指代表示地点的先行词。
1. I was born in a town in the 1960s 中的先行词是 表示年代的 1960s，不是而不是表示出生地点 town，所以要用 when，而不能用 where。
2. Every year sees the largest migration on the planet 先行词是表示时间的 every year，而不是表示地点是 planet，所以也不能用 where。

Answer 2

I was born in a town in the 1960s，when...

when引导定语从句，先行词是1960s, 后面应该是讲当年的情况

用where也未尝不可，先行词应该用the town（因为特指）

I was born in the town in the 1960s, where my father was also born.

第二句when引导定语从句，先行词是every year; 

如果用where，先行词就是planet

应该根据句意及结构判断先行词。

另外：这两题是哪年哪个地方的高考题呢？

Answer 3

先行词是时间用when，先行词是地点用where
第一句先行词是1960s，第二句先行词是every year