Answer:
A- the diary of a Jewish prisoner at Auschwitz
Step-by-step explanation:
The Nuremberg trials were when they charged Nazi officers and soldiers and charged them for crimes against the Jewish people. Auschwitz was a concentration camp, where Jews were held and killed. Even though very few Jews survived from there to tell the courts what happened, a diary of events from a person directly involved qualifies as a primary source.
(A secondary source, for example, is a person who heard about it from someone who was there, but was not actually present for the event.)