Read the passage below from Barack Obama's 2013 speech at the Buchenwald Concentration Camp. Which of the following conclusions is supported by this passage?
My great uncle's commander, General Eisenhower, understood this impulse to silence. He had seen the piles of bodies and starving survivors and deplorable conditions that the American soldiers found when they arrived, and he knew that those who witnessed these things might be too stunned to speak about them or be able — be unable to find the words to describe them; that they might be rendered mute in the way my great uncle had. And he knew that what had happened here was so unthinkable that after the bodies had been taken away, that perhaps no one would believe it.
— Barack Obama, Buchenwald Concentration Camp, 2013
A. American soldiers who liberated extermination camps were unaware of how horrible the Holocaust had been.
B. Nazi leaders had been extremely thorough in covering up the evidence of genocide in extermination camps.
C. The United States had gone to war with Nazi Germany in order to free prisoners being killed in extermination camps.
D. The liberation of Nazi extermination camps confirmed that groups other than Jews had been targeted by the Nazis.