Answer:
I regularly change shape yet remain a sphere. I am always there but not often seen. What am I?
What two keys cannot open any door?
I have cities but no houses I have mountains but no trees I have water but no fish. What am I?
My teeth help me suck.
If you've got me I'm everywhere. If you share me I'm nowhere. What am I?
I flow from the Homerβs mouth when he sees doughnuts.