The correct answer is D) They denounced and criticized the camps.
The Allies reacted when they discovered the Nazi concentration camps in the following way: They denounced and criticized the camps.
Indeed, when Allied troops found the concentration camps built by the Nazi Party, following the orders of Adolph Hitler, they were horrified for what they saw there. They did not expect to find the number of dead prisoners in the gas chambers. There were crops everywhere. When the world knew about the concentration camps and the persecution of Jews by the Nazis, people were in shock.