Your answer is D, i just did this one so 100% correct
That sentence is an example of parallel structure.
When there is repetition of a specific grammatical form in a sentence, parallelism or a parallel structure is produced. This occurs when you mantain the same pattern for every compared word or idea in your construction. This makes the idea easier to follow by the reader.
Answer:
The book has already been discussed by them.
Hope this helps!
