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.