The statement that best compares the work done by Leni Riefenstahl and Frank Capra to promote propaganda campaigns in their respective nations is:
Riefenstahl and Capra directed documentaries that supported the war effort in Germany and the U.S.
Both filmmakers created influential documentary-style works that were used for propaganda purposes during World War II, with Riefenstahl's films supporting the Nazi regime and Capra's films promoting American patriotism and support for the war effort.