关于which,who,that,

关于which,who,that,
The only one __ I want.
The most beautiful flower __on the park.
这里的两个空分别填什么?
which,who,that,whom,where等在定语从句呵宾语从句的用法.
My mum was the first one ___ told me that I was a good boy.这里用who或that都可以吗？