Question

when the nazi death camps were liberated, people around the world were most shocked by
the existence of the camps.
the size and scale of the camps.
the secrecy of the camps.
the locations of the camps.

Explanation:

While some awareness of Nazi camps existed, the full scope of their size, the industrialized mass murder system, and the sheer number of victims was not widely known until liberation. This large-scale, systematic brutality was the most shocking revelation for global audiences.

Answer:

the size and scale of the camps.