Many have heard it, but nobody has ever seen it. It will not speak back until spoken to. What is it? The answer to the riddle is an echo. Echo is the reflection of the sound that when it is released by the speaker, it arrives back to the speaker (now listener) but is delayed.
I think it is the a speaker's <span>behavior</span> knowledge both of the grammatical rules of a language and of the rules for appropriate use in social contexts Hope i helped you
