Complex sentence: It referes to Auschwitz concentration camp and it couldn't be true because the camp was liberated by The Red Army in 1945 and then Allies hadn't even crossed German river "Ren".
Split into simpler sentences: It referes to Auschwitz concentration camp which was liberated by The Red Army in 1945. It couldn't be true because then Allies hadn't even crossed German river "Ren".