The correct answer is the first option: the rationale for the Holocoust will always be incomprehensible.
The excerpt has many phrases and sentences that relate to understanding the reasoning behind the concentration camp called Birkenau. The Narrator claims that "[above] all, [survivors] tried to understand" why was it necessary for them to die in the concentration camps which the narrator calls "death factory".
In the end, the narrator concludes by saying "[perhaps] there was nothing to understand." This means that no matter how hard the narrator tries to find answers to his or her questions, maybe there was no sane reason for the existance of the concentration camp, Birkenau.
I think it would make sense for the author to agree with the fact that there's no logical explanation for the Holocaust.
