The correct answer is D. National leaders can be held responsible for crimes against humanity.
Statement A is incorrect because the precedent was set after World War I, almost three decades before the Nuremberg Trials.
Statement C is incorrect because defeated nations have been occupied by the victors in several wars before (like World War I).
Statement B is incorrect because the Nuremberg Trials punishes individuals who helped to organize the mass killings that took place during the Holocaust, even if they did not physically kill anyone.
This shows that only answer D. can be correct.
