During world war ii, the american military found that all its secret codes were being quickly deciphered by talented japanese code breakers.

the navajo language provided a unique solution. navajo was incredibly difficult to learn: complex, unwritten, and full of unusual and difficult sounds. so the military hired navajo "code talkers" to send top-secret messages.

the navajo "code" was not only secure, it was fast. with traditional codes, it could take hours to code and decode a message, but navajo soldiers could translate messages in just a few minutes.

the navajo code was never cracked. for many decades, the u. s. government kept the program a secret. but in 1968, the navajo soldiers' amazing contributions became known, and in 2001, the remaining code talkers received the congressional medal of honor.
which supporting detail from the passage is most important to include in a summary?

a.
the navajo language was never written down.

b.
the navajo language is very complex and difficult.

c.
the japanese code breakers were talented.

d.
the code talkers received a medal.