I believe the answer is: D. unsung Heroes
Unsung Heroes refers to the people in world war ii that never got the acknowledgement that they deserve for their important services during the war. One of the unsung heroes were the group that created the Navajo codes for US millitary to communicate with one another.
The codes were managed to intercepted by Japan, but due to the complexity of the navajo codes wich was made by native language prevented japan from deciphering it.
