We made this casserole using what was already in refrigerator. a our b ours c ourselves

The answer would be our, so A.

Hope this helps good luck

We made a casserole using what was already in our refrigerator

The correct answer is A, our.
B is incorrect as it is plural, referring to more than one refrigerator, when there is only one.
C is incorrect as it is plural referring to yourself, in which case yourself is not a refrigerator.