What is the main reason we use combinations of letters and numbers to stand for radio channels instead of saying the actual frequencies we use
a. The letters and numbers are "plain text" required by the Incident Command System
b. Other people aren't supposed to know the actual frequencies we are using and we do not want them to overhear us
c. The FCC requires secrecy on CAP frequencies
d. The actual frequencies are different in different CAP regions but the numbers and letters remain the same