Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: (CNN) When Peter MacDonald, Fleming Begaye and Thomas Begay joined the elite fraternity of Navajo Code Talkers during World War II, they had no idea what they were getting into. That was by design. The top-secret program they joined wouldn't even be declassified until more than two decades later -- long after the secret Navajo code language had played a vital role in the American war effort. All they knew at the time was that the Marines were recruiting and needed help from the Navajo people. "So we all volunteered. That's how he went in, that's how he went in, that's how I went in," said MacDonald, now 90, of his two comrades. MacDonald, Begaye and Begay were at the White House on Monday to receive praise for their service.The Navajo Code Talkers used their native language to invent a secret military codeThe code was vital to the US victory in the Pacific in World War II 
 Question:Those 29 _ created more than 200 new Navajo words for military terms and committed them to memory.

Navajo Code Talkers