Answer:
b. Discreteness
Explanation:
Displacement is how a language is capable of talking about things that are not immediately present. Duality is an old concept which believed that language was organized in two levels. Productivity is about how language can produce an infinite combination of sounds and meanings, basically.
Finally, discreteness is about pieces of the language that can be broken down and are not even perceived by natural speakers.
What do you need help with?
Supporting details can do all of the enlisted options except introduce the main idea. Supporting details are there to support the main idea, so of course they cannot introduce it. They are the result of the main idea, not its creator.
