Why Did the Allies Decide Not to Bomb the Rail

Why did the allies decide not to bomb the rail lines that serviced death camps such as Auschwitz?

A) They lacked the resources to commit to such an attack.
B) Stalin refused to grant US planes the right to use Soviet airbases.
C) The death camps were too far into German territory to be reached by Allied bombers.
D) Military strategists thought this would divert from the central task of defeating the Wehrmacht.