From a practical airmanship point of view, I would do the fuel drain check before each flight AND after each refuelling.
If your friendly refuellers had kindly uploaded you with a dose of water or other contaminant, in addition to the right stuff, it would be better to find out before you then go flying - and perhaps to advise the refuellers of your findings ? Also, I recommend that you do not assume that the previous pilot already did the 'first flight of the day' fuel drain check. Perhaps he did; he may even say he did, but ... Flight itself, with fuel sloshing around, may dislodge contaminants from a deteriorating tank system, so the next flight is always vulnerable.
As to the answer to the specific ATPL exam question, who can say ? They are notorious for weaselly wording ...
