Encoding,medium of transmission,decoding, and feedback
What context is the phrase used in…we can’t answer it for you without this
The word closest in meaning to copious is b - plentiful.
Copious is synonyms to bountiful and bountiful means abundance, plenty, overflowing and never lacking anything. The other choices are really different since all of it has the common ground in meaning which is opposite to the given word.
I believe your answer is The words modest and unimpressive impart a modest tone. Hope this helps!
-Lion