Final answer:
The United States decided to use the Navajo language as a basis for code during World War II because of its complex syntax, tonal qualities, limited speakers, and pre-existing written code.
Step-by-step explanation:
The United States decided to use the Navajo language as a basis for code during World War II because its complex syntax, tonal qualities, and limited speakers made it extremely difficult for enemy forces to decode. The Navajo language wasn't widely spoken, which provided an extra layer of security. Additionally, the Navajos developed a written code that the military was familiar with, known as the Navajo code talkers.
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