The code talkers work contributed mostly to

The code talkers contributed mostly to enhancing methods of coding secret  information.

Code talking was pioneered by the Cherokee and Choctaw people during World War 1.

The term code speakers refers to a group of people in the 20th century who utilized little known tribal languages as a mean of secret communication during war time.

The Marine Corps recruited the Navajo Code Talkers in 1941 and 1942. Twenty night people from the Navajo tribe were asked to develop a code within their language. They used their everyday tribal languages to convey classified messages. There was a special Navajo word for each letter of the English alphabet. After this, A Code Talking school was established and 400 more Navajos recruited. They had to complete an extensive training in communication and memorizing the code.

the three answers (for plato at least) are:

b-condemned sola fida 

d-set rules for establishing seminaries and for educating clerics in the seminaries 

f-recommended moderation in the sale of indulgences and banned the sale of false indulgences 

i also think it is c