You need to take the it's and put it where the
its is. And take the its in the original sentence and
put it where the it's is. It's is a contraction; it
is not a possessive. If you can't replace it with
It is, then it's its.
It's all perfectly clear, right? Here's the way to do it:
4. It's beginning to look a lot like Christmas at the University of Oregon, which has its Ducks in a Rose Bowl.