Which one is the right answer? I can't tell I think it's C

PART A: Which statement identifies the central idea of the text?

A. The Auschwitz concentration camp was the most inhumane of the camps, as it was the only one with a killing center.

B. Not all of the Auschwitz concentration camps treated prisoners inhumanely.

C. Despite the differing purposes of the three main camps of Auschwitz, they all treated prisoners inhumanely.

D. The Auschwitz concentration camps provided prisoners with the means to live, so they could provide useful labor