The code talkers used the Navajo's native language as it was already a "set" language and, with people in the US armed forces who have Navajo background and know how to talk it, well, you didn't have to train people to learn the code. This solved two problems, in which #1, already a group of people already knew how to speak it, which means less training, money spent on training, etc, and #2, the Japanese were baffled by how the US could use a native american language as a code, which meant that the Japanese couldn't break it, because it had no relations to other writings
hope this helps
While all 3 of B, C, and D played some roll in their decisions, C and D are the only to possible ones in my eyes as secession was not a hot button issue until Carolina's calls for it. I'd reckon it's a 50-50 between C and D, so I'd choose D.
The fact that the left column has less significant change than the one on the right might be because of several factors. As the years pass by, the regulation of air pollutants has improved drastically. Air quality has shown great progress during years thanks to things such as 1-less use of toxic raw material or fuels, 2- less use of polluting industrial processes, 3- controlling transport-related emissions, 4-improvement of clean air technology center gadgets like mechanical collectors and fabric filters, 5- development of control and monitoring strategies.
These shows evidence that it has been a lot of change in the air quality results but the charts show less reducing regulations because there are fewer pollutants in the air. The levels of carbon monoxide, lead and nitrogen dioxide had dropped because there is less of it in the air so the "change" is less because there is less to be changed thanks to the improvement on air polluting regulations.
The nation of Islam is where these two groups of Muslims coexisted
current day Iraq contains majority Sunni
Current day Pakistan contains majority Shi'te