Now that C (kitchen door) has been well established as the only correct choice, I īll add that we sometimes say "the door to the kitchen" (not "of") in specific situations.
I stayed in the dining room because the door to the kitchen was stuck.
Here are the basement steps and that is the door to the kitchen.
It īs a rather fine point, but we use this expression when we are emphasizing the passage to another place, rather than the door itself.
We painted the kitchen door white.
He asked me which is the door to the kitchen.
Did you close the attic door?
The door to the attic was always a thing of wonder to him.
I hope you can see the difference (if you care).
Bruce