It is a complex sentence because it is an independent idea and a dependent idea in one sentence.
I would say that all scenarios that are not too complex could be a basis for a short story, but also in principle, you could shorten and simplify any story to make a short story out of it!
So there is no clear distinction.
But among the options, the better candidates are:
a championship basketball game in which a new player is the star
a family mix-up over selecting a birthday present for Dad
the mysterious disappearance of a cake from the pantry
The other options are potentially too complex.
The Mouse in "If you give a mouse a cookie", he has a cookie and wants the other thing afterwards. Three qualities the mouse has is he is smart, sometimes greedy and cravings
