Question

the military code - talking system refers to
strict rules about how soldiers behave.
secret languages used for communication.
the special technique of pronouncing letters and numbers.
the chain of command ranking structure of the armed forces

Explanation:

A military code - talking system is about using secret languages (codes) for communication. It's not about behavior rules (strict rules about how soldiers behave), pronunciation techniques (the special technique of pronouncing letters and numbers), or command structure (the chain of command ranking structure of the armed forces).

Answer:

secret languages used for communication.