怎样判断非限定性定语从句的which 指代的是前面的句子 还是某个词?

看句子意思呀，比如：
1)He gave me a toy bear as birthday present, which made me very happy.
2)He gave me a toy bear on my birthday, which is a present I was longing for.
很显然第一句指代前面句子，因为是他送我礼物这件事情让我高兴，
而第二个句子是指代那个玩具熊，因为我想要的礼物是这个玩具熊。

这个要根据题意来看，都有可能啊
比如，1 . It rained heavily this morning, which made me late for school.
2. I came across a tiger yesterday, which was trapped in a cage.
1. 就是前面整句话，2就是前面的一个词

都有可能，现读便句子，再根据常识经验判断。

which 前面有逗号就是指代句子，反之是词

这么学语言多没劲啊。。。