What if one answered with "I answered that question already" -- would they be forced to come up with new questions?
Polygraph "examinations" aren't testimony where you are sworn to tell the truth, the whole truth, and nothing but the truth; nor are they actually a mechanism of "detecting lies" (a task at which they are ludicrously useless, per all research); they are psychological ordeals which are employed solely to create stress and cause people to break if they have anything to hide.